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+Project Gutenberg's The Baculum in Microtine Rodents, by Sydney Anderson
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: The Baculum in Microtine Rodents
+
+Author: Sydney Anderson
+
+Release Date: November 15, 2011 [EBook #38021]
+
+Language: English
+
+Character set encoding: ISO-8859-1
+
+*** START OF THIS PROJECT GUTENBERG EBOOK THE BACULUM IN MICROTINE RODENTS ***
+
+
+
+
+Produced by Chris Curnow, Alex Gam, Joseph Cooper and the
+Online Distributed Proofreading Team at http://www.pgdp.net
+
+
+
+
+
+
+
+  UNIVERSITY OF KANSAS PUBLICATIONS
+  MUSEUM OF NATURAL HISTORY
+
+  Volume 12, No. 3, pp. 181-216, 49 figs.
+
+  February 19, 1960
+
+  The Baculum in Microtine Rodents
+
+  BY
+  SYDNEY ANDERSON
+
+  UNIVERSITY OF KANSAS
+  LAWRENCE
+  1960
+
+  UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY
+
+  Editors: E. Raymond Hall, Chairman, Henry S. Fitch,
+  Robert W. Wilson
+
+  Volume 12, No. 3, pp. 181-216, 49 figs.
+  Published February 19, 1960
+
+  UNIVERSITY OF KANSAS
+  Lawrence, Kansas
+
+  PRINTED IN
+  THE STATE PRINTING PLANT
+  TOPEKA, KANSAS
+  1960
+
+[Illustration]
+
+  28-774
+
+
+
+
+The Baculum in Microtine Rodents
+
+BY
+
+SYDNEY ANDERSON
+
+INTRODUCTION
+
+
+Didier (1943, 1954) has described the bacula of several Old World
+microtines, and other rodents. Argyropulo studied (1933a, 1933b) five
+species of Cricetinae and _Microtus socialis_. Ognev (1950) illustrated
+numerous species of Eurasian microtines. Hamilton (1946) figured and
+described the baculum of 11 species of North American microtines. Hibbard
+and Rinker (1942, 1943) figured the baculum of _Synaptomys cooperi
+paludis_ and of _Microtus ochrogaster taylori_. Dearden (1958) studied
+the baculum in two Asiatic species of _Lagurus_, in six subspecies of
+_Lagurus curtatus_ of North America, and in six other species of
+microtines of other genera.
+
+The baculum can be preserved easily with standard study skins, and is
+potentially useful in interpreting relationships on any taxonomic level,
+and especially in determining the relationships of species within a
+genus, if used together with other structures.
+
+The anatomical orientation of the baculum needs comment because some
+confusion exists in the literature, especially concerning the use of the
+terms ventral and dorsal. The urethra lies on the anatomically ventral
+side of the penis, and of the baculum. In the center of the penis lies a
+single corpus cavernosum penis, shown in cross section proximal to the
+baculum in Figure 1c. Dorsally an artery, thinner walled than the ventral
+urethra, ends in a somewhat reticulate sinus surrounding primarily the
+middle part of the baculum within the bulbous glans penis. The corpus
+cavernosum penis (the structure has no median septum, at least distally)
+terminates with the baculum and is closely knit to it. The site of this
+bond is evident in the tuberosities and sculpturing of the base of the
+baculum.
+
+The part of the penis enclosing the baculum, when not erect, is folded
+back as shown in Figures 1a and 1b. As a result the anatomically ventral
+surface faces upwards, or at least posterodorsally. The use of the term
+ventral in this account refers to the anatomically ventral side, that is
+to say to the side of the baculum facing the urethra.
+
+The baculum in microtines consists of an elongate stalk, having a
+laterally, and to a lesser extent dorsoventrally, expanded base and an
+attenuate distal shaft. Usually, three digitate processes of
+cartilaginous material in which additional ossifications may occur arise
+from the terminus of the shaft. The proportions and curvature of the
+stalk vary as do the proportions of the terminal ossifications to each
+other and to the stalk. In some species one or more of the digital
+processes are frequently completely unossified.
+
+[Illustration: FIGURE 1. The baculum in _Microtus
+ochrogaster_--orientation and variation with age. _a._ Diagram of a
+sagittal section of the posterior half of a vole, natural size. The
+penis, containing the baculum (in black), extends ventrally from a point
+posterior to the pubic symphysis (stippled), along the body wall, and
+bends posteriorly at the distal end. _b._ Distal end of penis (× 2)
+showing baculum (in black), the urethra (solid lines) adjacent to the
+baculum, and the corpus cavernosum (broken lines) proximal to the
+baculum. _c._ Oblique view of the cross section of penis (× 4) shown in
+Figure 1 _b_. The thick-walled urethra lies ventral to the curved corpus
+cavernosum. A thinner-walled blood-vessel lies dorsal to the corpus
+cavernosum. The anatomically ventral side of the baculum, in the normal
+non-erect penis shown, is seen to face dorsally. _d._ Graph showing the
+relationship between size of baculum, size of animal, and development of
+digital ossifications. Circles show presence of ossification in stalk
+only; circles enclosing dots indicate presence of secondary ossification
+in median process also; large dots indicate the addition of tertiary
+ossification in one or both of the lateral digitate processes.]
+
+Preserved specimens of _Microtus arvalis_, _Microtus agrestis_, _Microtus
+orcadensis_, _Microtus nivalis_, _Microtus guentheri_, _Microtus
+subterraneus_, _Clethrionomys glareolus_, and _Ellobius lutescens_ were
+provided by Prof. Robert Matthey of Lausanne, Switzerland. J. Knox Jones,
+Jr. carefully saved the bacula with specimens of _Microtus fortis_ and
+_Clethrionomys rufocanus_ from Korea. Dr. W. B. Quay, Department of
+Zoology, University of California, supplied specimens of _Synaptomys
+cooperi_, _Phenacomys intermedius_, and _Microtus oregoni_. Dr. Franklin
+Sturges and Mr. John W. Goertz, Museum of Natural History, Oregon State
+College, Corvallis, have provided specimens including bacula of
+_Clethrionomys occidentalis_, _Microtus oregoni_, and _Microtus
+townsendii_. Dr. Randolph L. Peterson and Mr. Bristol Foster, Royal
+Ontario Museum of Zoology, Toronto, Canada, provided specimens of
+_Phenacomys intermedius_. Dr. J. N. Layne, University of Florida,
+Gainsville, Florida, presented me with a baculum of _Microtus parvulus_.
+
+I am indebted to all of these persons for their aid, and to various
+collectors for the Museum of Natural History, who preserved bacula with
+specimens. Many of these specimens were obtained through the assistance
+of the University of Kansas Endowment Association and the National
+Science Foundation.
+
+
+
+
+METHODS
+
+
+Bacula were obtained from fresh specimens, specimens preserved in alcohol
+or formalin, and dried study skins. The processing of bacula has been
+discussed by Hamilton (1946), Friley (1947), White (1951), and Dearden
+(1958). The methods used to preserve bacula for my study differed some
+from any of those reported. The terminal part of each penis including the
+baculum imbedded in the glans penis was removed in its entirety and
+placed in a vial. The catalogue number was kept with each specimen at all
+times. A two per cent solution of potassium hydroxide was added. All
+specimens were examined at least once a day. If tissues other than the
+glans penis were present they were removed with forceps when softened
+usually at the end of one day. Several drops of Alizarin red-S stain in a
+saturated alcoholic solution were added to the 3 to 5 ccs. of KOH
+solution in each vial. Solutions were replaced if they became turbid
+enough to obstruct observation of the clearing penis. After one day the
+solution containing stain was removed and replaced with two per cent KOH
+solution without stain. When the glans became sufficiently cleared that
+the stained baculum could be seen easily, the solution was replaced by
+glycerin in which clearing was completed. The time required for the
+entire process varied from one day to more than two weeks depending on
+the size of the specimen and on its condition. Fresh specimens clear more
+rapidly than dried specimens, and those that are dried more rapidly than
+those that are preserved. A three or four per cent solution of hydroxide
+will hasten the process, but more frequent observation is required to
+prevent excessive maceration.
+
+Specimens were then examined in a shallow dish containing glycerin under
+a binocular microscope. The baculum can be viewed from any desired
+direction. The method described above leaves the baculum intact within
+the glans penis; therefore its orientation can be determined relative to
+the thick walled urethra and the thin walled dorsal artery that extends
+onto the dorsal side of the baculum. The ventral curvature of the penis
+proximal to the baculum, and the distal extension, characteristic of most
+species, of the dorsal border of the glans (both shown in Figure 1) are
+other features aiding in correctly orienting cleared specimens. The
+digitate processes are not so often injured, lost, or displaced when the
+method described above is used as they are when the penis is dissected.
+Specimens were stored in glycerin in glass shell vials having
+polyethylene stoppers. A small card bearing the name, number, locality,
+and other data was placed in each vial. A specimen thus enclosed can be
+kept indefinitely, or removed and mounted in balsam as described by White
+(1951:631) or in plastic as described by Dearden (1958:541) and thus
+stored in the vial containing the skull of the specimen.
+
+Drawings were made on millimeter ruled paper while the baculum was viewed
+under a binocular microscope with a square ruled eyepiece.
+
+Unless otherwise noted all specimens listed are in the University of
+Kansas Museum of Natural History. Catalogue numbers are cited.
+Measurements are accurate to within less than one-tenth of a millimeter.
+Proportions as stated in the text are approximations, accurate to within
+one-twelfth (8.33 per cent). The range of variation is unknown for some
+species. Mention is made if maturity is known or suspected to differ in
+specimens being compared.
+
+The development of the baculum has been studied by Callery (1951) in
+_Mesocricetus auratus_ and by Ruth (1934) in the laboratory rat. In the
+rat (_Rattus norvegicus_) the bone is of endoblastemal origin being laid
+down by a condensation of undifferentiated mesenchymal cells. At the
+distal end of the bone dense fibrous tissue is then differentiated and at
+the proximal end hyaline cartilage. Growth is by substitution at the
+proximal end and by subperiosteal lamellation circumferentially. A marrow
+cavity is formed by resorption. In the baculum of the hamster the primary
+center of ossification is in the stalk, and is present at the age of
+three days; the secondary centers are in lateral processes and are
+present at 80 days and enlarge subsequently. A tertiary center, in each
+median process, may or may not develop later. Maximum development of the
+baculum is reached late in the reproductive life of the hamster.
+
+The early ossification of the baculum noted in the rat and the hamster
+occurs in _Microtus_ also. A specimen of _Microtus montanus fusus_
+(76831, from 5 mi. N, 26 mi. W Saguache, 9600 ft., Saguache County,
+Colorado) only 74 mm. in total length and weighing only 6.6 grams, had a
+slender ossified baculum having enlarged ends. This vole was one-half of
+the average length and less than one-fifth of the average weight of an
+adult, and of approximately the size at which weaning takes place.
+
+The development of the baculum in _Microtus ochrogaster_ was studied in
+32 specimens of various ages. The specimens (between Nos. 74994 and
+75074) were collected between August 15 and September 4, 1957, at
+localities on the Great Plains. These specimens were from breeding
+populations, as evidenced by pregnancy of females and by large size of
+testes of males. The length and width of the stalk of the baculum, the
+presence of digital ossifications, the total length of the animal, and
+the size of the testes were noted. Variability in length of testes is
+greatest when voles are from 140 to 150 mm. in total length. Sexual
+maturity is reached rather abruptly when the total length of most
+individuals is 140 to 150 millimeters. If the baculum likewise underwent
+more rapid growth at the onset of sexual maturity, greater variability
+should be evident in the length of the baculum of voles 140 to 150 mm. in
+total length than in bacula of voles of other sizes. This was the case
+(see Figure 1d). The baculum does not, however, suddenly reach its
+maximum maturity.
+
+The primary ossification is in the stalk. The secondary ossification is
+in the median process except in _Lagurus_ (Dearden, 1958:551) and some
+individuals of _Neofiber_ (see account on page 258). Tertiary centers of
+ossification are in the lateral processes. The primary ossification is
+present at an early age and subsequently increases in size and solidity.
+The secondary and tertiary ossifications are progressively more common in
+older voles. The increase in degree of ossification of all parts
+continues after sexual maturity is reached. Individual variation and
+variation with age in the baculum of _Microtus pennsylvanicus_ have been
+illustrated by Hamilton (1946:380). Figures 14, 15, and 17 illustrate
+variation with size, which is correlated with age, and also illustrate
+individual variation. The three bacula are from adult voles having testes
+that measured 15, 16 and 16 mm. in length, respectively. Each vole was
+trapped in late June. The total lengths in millimeters of the three voles
+are 172, 167, and 181; weights are 55, 52.4, and 65.5 grams. I judge that
+the greater size of the stalk and the better developed base shown in
+Figure 17 than in Figure 15 are illustrative of age variation; the
+difference in the size of the lateral digitate processes is, in this
+case, attributable to individual variation. Differences in the distal end
+of the baculum in Figures 42 and 43, show individual variation also.
+Figures 35 and 36 represent two different subspecies; different
+individuals of _M. mexicanus mogollonensis_, however, exhibit individual
+variation of the same degree.
+
+Hall and Cockrum (1953) list 44 species of microtines in North America.
+At least twelve of these are insular or local forms perhaps derived from
+some other species; for example _Microtus coronarius_, an insular form
+derived from _Microtus longicaudus_; _Microtus provectus_, considered by
+Chamberlain (1954:587) and by Wheeler (1956:176) as a subspecies of
+_Microtus pennsylvanicus_; and _Microtus ludovicianus_, a close relative
+of _Microtus ochrogaster_.
+
+All North American genera have been studied. Of the genus _Microtus_ in
+North America, all subgenera but _Orthriomys_ and all species but the
+following nine, have been studied: _M. (Orthriomys) umbrosus_, the
+insular _M. (Stenocranius) abbreviatus_, _M. (Microtus) breweri_, _M.
+(Microtus) nesophilus_, _M._
+
+[Illustration: FIGURES 2-13. Bacula of microtines. Unless indicated
+otherwise views are (_a_) of the dorsum, (_b_) the right side, and (_c_)
+the proximal end with the dorsal surface upward. Exact localities are
+given in accounts of species concerned.
+
+2. _Lemmus trimucronatus_, 50678, Point Barrow, Alaska.
+
+3. _Dicrostonyx groenlandicus_, 50539, Porcupine Lake, Brooks Range,
+Alaska.
+
+4. _Dicrostonyx groenlandicus_, 52524, Point Barrow, Alaska.
+
+5. _Synaptomys cooperi saturatus_, WBQ 3-C-454, 3 mi. S Demotte, Indiana.
+
+6. _Synaptomys cooperi paludis_, 13716, Meade County State Park, Kansas.
+
+7. _Phenacomys intermedius celatus_, SA 2044, Quebec.
+
+8. _Phenacomys intermedius intermedius_, WBQ 3-C-309, 5.4 mi. S Moran,
+Teton Co., Wyoming.
+
+9. _Clethrionomys rufocanus_, 60438, 1 mi. NW Oho-ri, Korea, (_d_)
+ventral view.
+
+10. _Clethrionomys gapperi_, 42108, 31 mi. N Pinedale, Wyoming.
+
+11. _Clethrionomys rutilus_, 42865, 5 mi. NNE Gulkana, Alaska.
+
+12. _Clethrionomys occidentalis_, FWS 30, Mary's Peak, Benton Co.,
+Oregon.
+
+13. _Clethrionomys glareolus_, 67100, Zermatt, Valais, Switzerland.]
+
+[Illustration: FIGURES 14-25. Bacula of _Microtus_. Unless indicated
+otherwise views are (_a_) of the dorsum, (_b_) the right side, and (_c_)
+the proximal end with dorsal surface upward.
+
+14. _M. pennsylvanicus_, 42439, 1 mi. S, 2 mi. E Eagle Nest, Colfax Co.,
+New Mexico; abnormality perhaps owing to injury; dorsal view.
+
+15. _M. pennsylvanicus_, 42306, 5 mi. N, 26 mi. W Saguache, Colorado;
+dorsal view.
+
+16. _M. pennsylvanicus_, 43043, 20 mi. NE Anchorage, Alaska, ventral
+view.
+
+17. _M. pennsylvanicus_, 42430, 1 mi. S, 2 mi. E Eagle Nest, New Mexico.
+
+18. _M. agrestis_, 67102, Gryon, Switzerland.
+
+19. _M. montanus amosus_, 62241, 1/2 mi. E Soldier Summit, Wasatch Co.,
+Utah.
+
+20. _M. montanus nanus_, 57470, 2 mi. N, 2 mi. W Pocatello, Idaho.
+
+21. _M. montanus fusus_, 42307, 5 mi. N, 26 mi. W Saguache, Colorado.
+
+22. _M. arvalis_, 67101, Vidy, Switzerland, possibly not mature.
+
+23. _M. guentheri_, 67104, Palestine.
+
+24. _M. orcadensis_, 67106, Orkney Islands, orientation uncertain.
+
+25. _M. fortis_, 63841, Chipo-ri, Korea, (_d_) ventral view.]
+
+[Illustration: FIGURES 26-39. Bacula of microtines. Unless indicated
+otherwise views are (_a_) of the dorsum, (_b_) the right side, and (_c_)
+the proximal end with the dorsal surface upward.
+
+26. _M. (Pitymys) fatioi_, 67103, Zermatt, Switzerland, immature.
+
+27. _M. (Pitymys) pinetorum_, 76834, 2 mi. N Baldwin, Douglas Co.,
+Kansas.
+
+28. _M. (Pitymys) pinetorum_, 68545, 1 mi. NE Pleasant Grove, Kansas.
+
+29. _M. (Pitymys) quasiator_, 30709, Teocelo, Veracruz, (_d_) ventral
+view.
+
+30. _M. (Pitymys) quasiator_, 19878, 5 km. N Jalapa, Veracruz.
+
+31. _M. (Pedomys) ochrogaster_, 75036, 1 mi. N, 2 mi. E Oberlin, Kansas.
+
+32. _M. (Stenocranius) miurus_, 51152, Lake Schrader, Brooks Range,
+Alaska.
+
+33. _M. (Stenocranius) miurus_, 51169, Lake Schrader, Brooks Range,
+Alaska.
+
+34. _M. (Stenocranius) gregalis_, 8059, "Eastern Europe."
+
+35. _M. mexicanus mexicanus_, 63094, Valle de Bravo, Estado de México,
+México.
+
+36. _M. mexicanus mogollonensis_, 63298, Mt. Taylor, Valencia Co., New
+Mexico.
+
+37. _M. californicus_, 76828, 1 mi. NE Berkeley, California; (_d_)
+ventral view.
+
+38. _M. (Arvicola) richardsoni_, 42454, 31 mi. N Pinedale, Sublette Co.,
+Wyoming.
+
+39. _M. richardsoni_, 37903, 23-1/2 mi. S, 5 mi. W Lander, Wyoming;
+distal end.]
+
+[Illustration: FIGURES 40-49. Bacula of microtines. Unless indicated
+otherwise views are (_a_) of the dorsum, (_b_) the right side, and (_c_)
+the proximal end with the dorsal surface upward.
+
+40. _Microtus (Pitymys) parvulus_, UF 1508, 1 mi. W Micanopy, Florida.
+
+41. _Microtus townsendii_, 79186, Sec. 33, T. 11S, R. 5W, Benton Co.,
+Oregon.
+
+42. _Microtus (Herpetomys) guatemalensis_, 65895, 2 mi. S San Juan Ixcoy,
+Guatemala.
+
+43. _M. guatemalensis_, 65921, 10 mi. E, 4 mi. S Totonicapan, Guatemala,
+dorsal view of tip.
+
+44. _Microtus oeconomus_, 43048, Kelsall Lake, British Columbia.
+
+45. _Microtus (Chilotus) oregoni_, WBQ 3-C-248, 5 mi. N Orick,
+California.
+
+46. _Lagurus (Lemmiscus) curtatus_, 26053, 9 mi. S Robertson, Uinta Co.,
+Wyoming.
+
+47. _Microtus (Chionomys) nivalis_, 65127, Wetterstein, Germany,
+orientation uncertain.
+
+48. _Microtus (Chionomys) longicaudus_, 50253, Crane Flat, Mariposa Co.,
+California.
+
+49. _Neofiber alleni_, 27268, 2 mi. S Gainesville, Florida, orientation
+uncertain.]
+
+(_Microtus_) _provectus_ (the last three are probably insular derivatives
+of _M. pennsylvanicus_), _M._ (_Microtus_) _fulviventer_ (perhaps derived
+from the same stock as _Microtus mexicanus_), _M._ (_Microtus_)
+_xanthognathus_ (perhaps related to _Microtus chrotorrhinus_), _M._
+(_Microtus_) _coronarius_, and _M._ (_Pedomys_) _ludovicianus_.
+
+
+SPECIES OF WHICH BACULA WERE EXAMINED
+
+  Subfamily: Microtinae                              Number of Specimens
+    Tribe: Lemmi
+      _Dicrostonyx groenlandicus_ (Traill)                   4
+      _Lemmus trimucronatus_ (Richardson)                    6
+      _Synaptomys cooperi_ Baird                             5
+    Tribe: Microti
+      Genus: _Clethrionomys_ Tilesius, 1850
+        _Clethrionomys rutilus_ Pallas                       4
+        _Clethrionomys gapperi_ (Vigors)                     9
+        _Clethrionomys occidentalis_ (Merriam)               1
+        _Clethrionomys glareolus_ Schreber                   1
+        _Clethrionomys rufocanus_ Sundevall                  1
+      Genus: _Phenacomys_ Merriam, 1897
+        _Phenacomys intermedius_ Merriam                     5
+      Genus: _Ondatra_ Link, 1795
+        _Ondatra zibethicus_ (Linnaeus)                      1
+      Genus: _Microtus_ Schrank, 1798
+        (_Herpetomys_) _guatemalensis_ Merriam               3
+        (_Arvicola_) _richardsoni_ (DeKay)                   2
+        (_Chilotus_) _oregoni_ (Bachman)                     3
+        (_Stenocranius_) _gregalis_ (Pallas)                 1
+        (_Stenocranius_) _miurus_ Osgood                     9
+        (_Chionomys_) _longicaudus_ (Merriam)                6
+        (_Chionomys_) _nivalis_ Martins                      2
+        (_Microtus_) _arvalis_ (Pallas)                      1
+        (_Microtus_) _orcadensis_ Millais                    1
+        (_Microtus_) _guentheri_ Danford and Alston          1
+        (_Microtus_) _fortis_ Büchner                        2
+        (_Microtus_) _montanus_ (Peale)                     15
+        (_Microtus_) _townsendii_ (Bachman)                  3
+        (_Microtus_) _oeconomus_ (Pallas)                   10
+        (_Microtus_) _mexicanus_ (Saussure)                 13
+        (_Microtus_) _californicus_ (Peale)                  2
+        (_Microtus_) _pennsylvanicus_ (Ord)                 13
+        (_Microtus_) _agrestis_ (Linnaeus)                   1
+        (_Pedomys_) _ochrogaster_ (Wagner)                  41
+        (_Pitymys_) _pinetorum_ (LeConte)                    2
+        (_Pitymys_) _parvulus_ (Howell)                      1
+        (_Pitymys_) _quasiater_ (Coues)                      5
+        (_Pitymys_) _fatioi_ Mottaz                          1
+      Genus: _Neofiber_ True, 1884
+        _Neofiber alleni_ True                               2
+      Genus: _Lagurus_ Gloger, 1841
+        _Lagurus curtatus_ (Cope)                            7
+
+           Total number examined                           184
+
+
+
+
+ACCOUNTS OF SPECIES
+
+
+Dicrostonyx groenlandicus (Traill)
+
+Figs. 3 and 4
+
+Baculum: stalk elongate, greatest length (3.1 mm.) 2-1/5 to 2-1/2 times
+greatest breadth, and 4-1/2 times greatest depth; digitate processes
+usually cartilaginous, occasionally lateral processes partly ossified;
+basal tuberosities weakly to moderately developed, medially confluent;
+posterior profile in dorsal view rounded with rounded posterior apex or
+shallow notch; dorsal concavity in end-view shallower and not so wide as
+ventral concavity; median constriction approximately 2/3 greatest depth;
+ventral part of base in end-view wider than dorsal part; shaft straight
+or slightly curved; base of stalk placed dorsally relative to axis of
+shaft; stalk spatulate, sometimes with distal enlargement; at mid-point
+stalk wider than high; lateral profile in dorsal view sloping gradually
+without abrupt curvature anterior to point of greatest width.
+
+The baculum of _Dicrostonyx torquatus_ figured by Ognev (1948:476) agrees
+with that of _D. groenlandicus_ in shape of stalk, and in lateral
+digitate processes that are small relative to size of median process; but
+differs in more elongate, terminally enlarged, bulbar shape of median
+process. None of my specimens showed ossification in the lateral
+processes, observed by Hamilton (1946:381) in _Dicrostonyx rubricatus
+richardsoni_ [ = _D. groenlandicus richardsoni_]. In all of my specimens
+the cartilaginous median process was larger than that figured by
+Hamilton, or by Dearden (1958:542).
+
+_Specimens examined_: Four from; Point Barrow, Alaska, 52524 (Barrow
+Village), 67264 (died in captivity); Brooks Range, Alaska, 50536 (Wahoo
+Lake, 69°08', 146°58'), 50539 (Porcupine Lake, 68°51'57", 146°29'50",
+3140 ft.).
+
+
+Lemmus trimucronatus (Richardson)
+
+Fig. 2
+
+Baculum: Stalk heavy, broad, greatest length (2.8 mm.) in mature
+individuals (Fig. 2) as little as 1-1/3 times greatest breadth, greatest
+length no less than 2-2/3 times greatest depth of base; three ossified
+processes, median one from as long as to 1/2 longer than the lateral
+processes, and approximately 2/3 wider and twice as deep as lateral
+processes; length of median process almost 3-1/2 times its breadth,
+approximately 1/2 length of stalk; basal fossae broadly confluent;
+posterior profile in dorsal view evenly rounded; in end-view ventral
+concavity deeper than dorsal concavity, constriction as little as 1/2
+greatest depth in mature specimens; shaft straight, bluntly rounded, or
+slightly decurved and laterally inflated terminally; lateral profile in
+dorsal view a gradual slope from widest point of stalk anteriorly onto
+shaft; in younger individuals stalk slenderer, otherwise as described
+above.
+
+Five specimens examined by me differ from one figured and described by
+Hamilton (1946:379) in that stalk is better developed, larger relative to
+size of processes, length of stalk in my specimen (Fig. 2) 2.8 as opposed
+to 2.1 mm. in Hamilton's specimen; median process shorter, 1.5 as opposed
+to 1.8 mm., proximal end rounded rather than concave, not partially
+enclosing tip of shaft; proportion of and relative sizes of median and
+lateral processes approximately same as in Hamilton's _Lemmus helvolus_
+[ = _Lemmus trimucronatus helvolus_]. A specimen figured by Dearden
+(1958:542) has a basally trilobed median process.
+
+The baculum of the Asiatic _Lemmus lemmus_ figured by Ognev (1948:413)
+agrees with my specimens in the ossification of three processes, the
+relative sizes of these processes to each other and to the stalk, the
+well-developed base of the stalk and heavy bluntly rounded shaft; the
+baculum of _Lemmus lemmus_ differs in greater anterolateral extent of
+basal tuberosities, in proximal notch seemingly separating these
+tuberosities, and in median process being slenderer.
+
+_Specimens examined_: Five, of two subspecies; _Lemmus trimucronatus
+alascensis_, Point Barrow, Alaska, numbers 50591, 50678, 50731, 50758;
+_Lemmus trimucronatus subarcticus_, Wahoo Lake, 69°08', 146°58', 2350
+ft., Brooks Range, Alaska, 50948.
+
+
+Synaptomys cooperi Baird
+
+Figs. 5 and 6
+
+Baculum: Stalk elongate, greatest length (2.7 to 2.8 mm.) 2-1/3 to 2-1/2
+times greatest breadth, 4 to 5 times greatest depth; three processes
+ossified or lateral processes unossified, ossifications relatively small
+(in 78380, median ossification less than 1/4 as large as lateral
+ossifications although median cartilaginous process is larger), length of
+median process 1/5 to 1/6 of length of stalk, cartilaginous part of
+median process larger; posterior profile in dorsal view convex throughout
+or bilobate; tuberosities moderately developed, deflected dorsal to axis
+of shaft; in end-view medial construction 3/5 greatest depth of
+tuberosities; shaft tapered from point of greatest width, slightly
+inflated terminally.
+
+The specimen (KU 13716) figured by Hibbard and Rinker (1942:29) has been
+restudied. It was first cleared and stained to soften the dry cartilage
+binding the digital processes together and to differentiate bone and
+cartilage. The lateral processes are small and cartilaginous (Fig. 6) and
+seem intact. The differences between this specimen and others examined by
+Hamilton (1946:381), Dearden (1958:542), and myself, namely the
+relatively larger median ossification, the absence of ossification in
+lateral processes, and the distinctly bilobate base and larger size, may
+represent geographic differences, or individual variation. The
+proportions of length, width, and depth of the stalk, and the appearance
+in lateral view do not differ greatly from others examined by Hamilton,
+by Dearden (1958:546), and by me.
+
+_Specimens examined_: Five, representing four subspecies; _S. cooperi
+gossii_, 6 mi. N Midway, Holt Co., Nebraska 78379, 78380; _S. cooperi
+relictus_, 5 mi. N, 2 mi. W Parks, Dundy Co., Nebraska, 72601 (immature);
+_S. cooperi saturatus_, 3 mi. S Demotte, Jasper Co., Indiana, 3-C-454,
+collection of W. B. Quay; _S. cooperi paludis_, Meade County State Park,
+Kansas, 13716.
+
+
+Clethrionomys rutilus Pallas
+
+Fig. 11
+
+Baculum: Stalk elongate, and proximally enlarged, greatest length (2.7
+mm.) 2 times greatest breadth; less than 4 times greatest depth; three
+well-developed ossified processes; length of stalk 2-1/3 times length of
+median process; median process with basal (and ventral) protuberence and
+lateral lobes, arched in dorsoventral plane; lateral processes as large
+as median process, flattened distally, having ventromedial vane on distal
+half; basal tuberosities of stalk well developed, medially confluent;
+posterior profile in dorsal view trilobate or convex throughout with
+rounded posterior apex; dorsal concavity well developed, ventral surface
+but slightly concave, medial constriction of base as little as 1/2
+greatest depth; shaft straight, slender, at mid-point of stalk but
+slightly wider than high; basal tuberosities largely dorsal to axis of
+shaft in lateral view; lateral profile in dorsal view with an abrupt
+curvature separating the gently sloping sides of the shaft from the basal
+part at its greatest breadth.
+
+The specimen of _Clethrionomys rutilus_ figured by Ognev (1950:120) is
+essentially like the North American specimens examined by me in the
+relative sizes of the ossifications and the general shape of the stalk.
+
+_Specimens examined_: Four, of one subspecies; _C. r. dawsoni_, west bank
+Gakona River, 1700 ft., 5 mi. NNE Gulkana, Alaska, 42865, 42866; SW end
+Dezadeash Lake, 2400 ft., Yukon Territory, 42910, 42921.
+
+
+Clethrionomys gapperi (Vigors)
+
+Fig. 10
+
+Baculum: Stalk elongate, greatest length (2.8 mm.) 1-3/4 times greatest
+breadth, and 3-3/4 times greatest depth; proximally enlarged, greatest
+depth 1/2 greatest breadth; three well-developed ossified processes;
+length of stalk 2-1/3 times length of median process; median process
+arched in dorsoventral plane, with basiventral protuberence or spine and
+lateral lobes; lateral processes as large as median process, flattened
+distally, arched; basal tuberosities of stalk well developed, medially
+confluent; posterior profile in dorsal view trilobate or convex
+throughout with a rounded posterior apex; dorsal concavity well
+developed, ventral surface but slightly concave, or in some cases
+slightly convex; medial constriction of base 3/5 greatest depth; shaft
+straight, slender, at mid-point of stalk twice as wide as high; basal
+tuberosities dorsally placed relative to axis of shaft; lateral profile
+in dorsal view abruptly curved anterior to point of greatest width;
+slender stalk distinct from angular enlarged base.
+
+The most noticeable difference between the baculum of _C. rutilus_ and
+_C. gapperi_ is size. The proportions of the four ossifications are
+approximately the same. Ventral vanes on the lateral processes are not
+developed in _C. gapperi_. _C. gapperi_ and _C. rutilus_ are more nearly
+alike in their bacula than any other two species of _Clethrionomys_
+examined. _Clethrionomys occidentalis_, the other New World species, is
+also much like _C. gapperi_ and _C. rutilus_. The differences are of a
+magnitude comparable to those between the bacula in subspecies of
+_Microtus montanus_ (Figs. 19-21) for example, or in subspecies of
+_Lagurus curtatus_ (Dearden, 1958:542).
+
+_Specimens examined_: Nine, of two subspecies; _Clethrionomys gapperi
+athabascae_, British Columbia, 42922 (Indian Creek, Mile Post 234 of
+Alaskan Highway), 64281 (West bank Racing River, 89 mi. W Muskwa), 64287
+(North bank Tetsa River, 56 mi. W, 11 mi. S Muskwa), 64290 (44 mi. W, 9
+mi. S Muskwa), 64310 (32 mi. W, 2 mi. S Muskwa); _Clethrionomys gapperi
+galei_, 31 mi. N Pinedale, Sublette Co., Wyoming, 42108; Grand Mesa,
+Delta Co., Colorado, 60014 and 60015 (5-1/2 mi. E, 12 mi. S Collbran),
+60022 (8 mi. E, 1/2 mi. S Skyway).
+
+
+Clethrionomys occidentalis (Merriam)
+
+Fig. 12
+
+Baculum: Stalk elongate, greatest length (2.8 mm.) 2-1/2 times greatest
+breadth, 6 times greatest depth; three well-developed ossified processes;
+median process larger than lateral processes, 1/2 the length of stalk,
+curved, basally broad, ventrally keeled, trilobate posteriorly; lateral
+ossifications large, flattened distally, curved; posterior profile of
+stalk posteriorly slightly emarginate, thus bilobate in outline; in
+end-view dorsal concavity deeper than ventral, constriction less than 1/2
+greatest depth, tuberosities confluent, visible in dorsal view at each
+side; shaft slender, especially in depth, straight; at mid-point of stalk
+almost twice as wide as deep, slight terminal inflation.
+
+The general proportions of the stalk and the relatively large, uniquely
+shaped processes, are characteristic of most specimens of the genus
+_Clethrionomys_ examined.
+
+_Specimen examined_: _C. occidentalis californicus_, one from Mary's
+Peak, Benton Co., Oregon, 30, F. W. Sturges' collection.
+
+
+Clethrionomys glareolus Schreber
+
+Fig. 13
+
+Baculum: Stalk elongate, greatest length (2.9 mm.) twice the greatest
+breadth in the specimen examined, flattened proximally, greatest length
+almost 6 times greatest depth of base; three well-developed ossified
+processes; median process arched in a dorsoventral plane, with basal
+notch and lateral lobes; lateral processes as long as median process,
+bowed in dorsal view, flattened distally, with ventromedial vane; basal
+tuberosities of stalk weakly developed, medially confluent; posterior
+profile in dorsal view evenly rounded; in end-view dorsal concavity
+shallow in comparison to most species but deeper than ventral concavity,
+constriction 3/4 greatest depth; shaft straight, at mid-point slightly
+wider than high, elongate, widest point of stalk less than 1/4 of total
+length from proximal end, slight lateral inflation at tip; lateral
+profile in dorsal view sloping at first abruptly and then gradually from
+widest point of stalk anteriorly onto shaft.
+
+The specimen of _Clethrionomys glareolus_ figured by Ognev (1950:31) in
+dorsal view as I interpret it, resembles my specimen in the rounded base;
+in the elongate, distally inflated shaft; in the initially abrupt slope
+of the lateral profile in dorsal view from the greatest width of stalk
+anteriorly; and in the presence of three well ossified processes. Ognev's
+specimen differs from mine in the median process being more elongate
+relative to its width, and rounded proximally, lacking lateral lobes and
+basal notch; in lateral processes being less curved; in the greater
+terminal inflation of the shaft; and in the closer approximation of the
+terminal processes to the shaft. The baculum of _Clethrionomys glareolus_
+as described and figured by Didier (1954:243-244) resembles my specimen
+in general proportions, but is more pointed proximally and more curved in
+dorsoventral plane. Didier states that the baculum is rather variable in
+form in this species, in different regions, but that a large number of
+specimens must be examined to assess the geographic nature of this
+variation.
+
+_Specimen examined_: One from Zermatt, Valais, Switzerland, 67100.
+
+
+Clethrionomys rufocanus Sundevall
+
+Fig. 9
+
+Baculum: Base of stalk broad but relatively flattened dorsoventrally,
+greatest length (3.2 mm.) less than 1-1/2 greatest width, 4 times
+greatest depth; three well-developed ossified processes; median process
+arched in dorsoventral plane, having basal notch and lateral lobes;
+lateral processes as long as median process, flattened distally, with
+ventromedial vane; basal tuberosities of stalk weakly developed, medially
+confluent; posterior profile in dorsal view convex with rounded posterior
+apex; dorsal surface of base almost flat, ventral concavity broad and
+shallow; constriction 3/4 greatest depth (not including an unusual
+irregularity on the ventral surface of the base); shaft straight, at
+mid-point of stalk distinctly wider than high, slender at distal end,
+widest point of stalk almost 1/3 of total length from proximal end, tip
+of shaft rounded; lateral profile in dorsal view gradually sloping from
+widest point anteriorly onto shaft.
+
+The specimen of _Clethrionomys rufocanus_ figured by Ognev (1950:97)
+resembles my specimen in the presence of three well ossified processes.
+Ognev's specimen differs however in the lack of a proximal notch on the
+median process, the lesser proportion of the stalk included in the basal
+enlargement, the more posterior position of the point of greatest width,
+and the presence of a concavity in the posterior profile of the stalk in
+dorsal view. These differences in the stalk may be owing to a difference
+in age (my specimen perhaps being older).
+
+_Specimen examined_: One from 1 mi. NW Oho-ri, 6 M., Korea, 60438.
+
+
+Phenacomys intermedius Merriam
+
+Figs. 7 and 8
+
+Baculum: Stalk slender, greatest length (2.9 mm.) 2-1/4 to 2-1/2 times
+greatest breadth, 4 times greatest depth; three well-developed ossified
+processes, median one almost 1/2 length of stalk, curved, broad basally
+and slightly larger in all dimensions than either lateral process;
+lateral processes flattened distally, curved; base of stalk well
+developed, basal tuberosities medially confluent or separated by medial
+emargination, posterolateral faces flattened or rough; emarginations in
+the four adults examined; posterior profile in dorsal view bluntly
+pointed or flattened except for emargination posterially, abruptly curved
+at point of greatest width; shaft arising broadly from distal side of
+base of stalk; in end-view hour-glass shaped, medial constriction
+pronounced, both dorsal and ventral concavities deep; shaft having
+relatively straight but distally convergent sides; at mid-point of stalk,
+1 to 1-1/2 times as wide as deep; tip bluntly rounded, or slightly
+inflated.
+
+The specimens from Quebec differ from the one from Wyoming in smaller
+size, relatively smaller lateral digital processes, larger more medial
+basal emargination, and slender shafts. The baculum of _Phenacomys
+intermedius_ differs much from that of _Phenacomys longicaudus_,
+described by Hamilton (1946:381) and by Dearden (1958:547). Dearden
+states that the three bacula examined by him of _Phenacomys longicaudus_
+differ markedly from the specimen described by Hamilton. It seems to me
+that in major features the resemblance is greater between the specimens
+of _Phenacomys longicaudus_ examined by these two authors than between
+their specimens and specimens of other microtines, including _Phenacomys
+intermedius_. Neither Hamilton nor Dearden record the exact localities of
+capture, the collections in which the specimens are deposited, or the
+catalogue numbers of specimens. Consequently verification of
+identifications and observations is difficult.
+
+_Specimens examined_: Five, of two subspecies; _P. intermedius
+intermedius_, 5.4 mi. S Moran, Teton Co., Wyoming, 3-C-309, collection of
+W. B. Quay; _P. intermedius celatus_, four (including one immature
+specimen) from Authiernord, Abitibi-ouest Co., Quebec, specimens in
+collection of Bristol Foster designated by numbers 2041-2044 of S.
+Anderson's field catalogue. Smith and Foster (1957:107) were of the view
+that _Phenacomys ungava_ (including the above specimens from Quebec) may
+be specifically distinct from _Phenacomys intermedius_.
+
+
+Ondatra zibethicus (Linnaeus)
+
+Not figured
+
+Baculum: In the single specimen examined, less mature than that figured
+by Hamilton (1946:384), the digitate processes are cartilaginous, the
+basal tuberosities are less well developed, and the shaft is slenderer
+throughout. The cartilaginous processes are of the same proportions as
+ossified processes in the figure mentioned. The shaft is also convex
+ventrally in lateral profile. The view of the side here considered to be
+anatomically the ventral side (adjacent to the urethra) is labelled
+dorsal view in Hamilton's specimen.
+
+_Specimen examined_: One, from Reserve, Brown Co., Kansas, 72405.
+
+
+Microtus (Herpetomys) guatemalensis Merriam
+
+Figs. 42 and 43
+
+Baculum: Stalk moderately elongate, greatest length (3.5 mm.) 2-1/3 times
+greatest breadth, spatulate, flattened throughout, greatest thickness 1/3
+millimeter; three ossified processes; median process having three
+cornered base, curved dorsally, wider than high, 1/4 to 1/5 greatest
+length of stalk; each lateral process bent at middle, as long as median
+process, compressed laterally; base of stalk curved dorsally,
+tuberosities marginal, hence narrow, lateral excavations of tuberous
+margin not confluent medially; in end-view ventral concavity broad, no
+dorsal concavity, medial constriction but slightly less than greatest
+thickness (not depth); shaft wider than high throughout, at mid-point
+more than 3 times as wide as high; tip of shaft slightly inflated both
+laterally and dorsoventrally; lateral profile gradually sloping
+anteriorly from widest point of stalk.
+
+Specimen number 65921 (Fig. 43) differs from number 65895 (Fig. 42)
+described above. Terminus of shaft of number 65921 has lateral lobes from
+which arise lateral cartilaginous processes; median terminal ossification
+irregular in shape, smaller, imbedded in terminally bilobate cartilage.
+In the spatulate flattened stalk these two specimens are much alike. An
+immature specimen, number 65908, is smaller (length of stalk 2.6 mm.)
+also flattened and spatulate, has the terminal processes cartilaginous,
+the lateral processes bent medially, and proportions as in the adult.
+
+The baculum shows no noteworthy resemblance to that of any other species
+of North American _Microtus_; on the other hand the differences between
+_M. guatemalensis_ and some other species are no greater than the
+differences between certain species included in the subgenus _Microtus_.
+The baculum neither strengthens nor weakens the case for subgeneric rank
+for _M. (Herpetomys) guatemalensis_.
+
+_Specimens examined_: Three from Guatemala; 65895 (2 mi. S San Juan
+Ixcoy), 65908, (3-1/2 mi. SW San Juan Ixcoy), 65921 (10 mi. E, 4 mi. S
+Totonicapán).
+
+
+Microtus (Arvicola) richardsoni (DeKay)
+
+Figs. 38 and 39
+
+Baculum: Stalk broad, greatest length (3.7 to 4.3 mm.) 1-1/2 times
+greatest breadth, relatively flattened, greatest depth 1/3 greatest
+breadth; single median ossified process, in smaller of two specimens this
+ossification incomplete and of unusual shape (Fig. 39); length of stalk 4
+times length of median process; concavities of basal tuberosities
+medially confluent, constriction less than 1/2 greatest depth; widest
+point of shaft less than 1/4 length of shaft from posteriormost point;
+shaft wider than high except at distal end that is inflated dorsally and
+sometimes laterally; both ventral and dorsal concavities of base of stalk
+broad and moderately deep; posterior profile in dorsal view evenly
+rounded or having marginal notch.
+
+In the absence of ossified lateral processes my two specimens differ from
+bacula of _Microtus (Arvicola) terrestris_ figured by Didier (1943:79,
+1954:245, 247, 248) and by Ognev (1950:591). The median process relative
+to the size of the shaft is smaller, and the shaft relative to its length
+is wider in _M. richardsoni_ than in _M. terrestris_. The stalk of _M.
+(Arvicola) amphibius_ figured by Didier is like that of _M. richardsoni_
+in its greater breadth and median notch on posterior border.
+
+The relationship of the New World water rat, _M. richardsoni_, to the Old
+World water rats (genus _Arvicola_ of some European authors) is
+uncertain. Miller (1896:66) placed all of them in the subgenus
+_Arvicola_. Subsequent authors, stressing differences in the teeth, have
+placed _M. richardsoni_ in the subgenus _Aulacomys_ of Rhoads. Zimmerman
+(1955) has shown that teeth in some _Arvicola_ approach the more complex
+pattern of _M. richardsoni_. He argues also that _Arvicola_ is
+generically distinct from _Microtus_ on the grounds that the two groups
+have separate origins, _Arvicola_ having descended from the genus
+_Mimomys_ and _Microtus_ from some other group of microtines. This
+argument also was advanced by Hinton (1926:47-48). Pending further
+studies of the possible polyphyletic origin of other subgenera of the
+genus _Microtus_, I refer both _M. richardsoni_ and _M. terrestris_ to
+the subgenus _Arvicola_.
+
+The evidence afforded by the bacula available is not conclusive as to
+relations of Old World and New World water rats. No general agreement on
+the number of species in this Palaearctic group has been reached, and
+bacula of only three or four of the numerous Old World subspecies have
+been figured. I have examined none.
+
+_Specimens examined_: Two, from Wyoming; 42454 (31 mi. N Pinedale, 8025
+ft., Sublette Co.), 37903 (23-1/2 mi. S, 5 mi. W Lander, 8600 ft.,
+Fremont Co.).
+
+
+Microtus (Chilotus) oregoni (Bachman)
+
+Fig. 45
+
+Baculum: Stalk broad, greatest length (2.2 mm.) 1-3/4 times greatest
+breadth, 3-1/2 times greatest depth; three well-developed ossified
+processes; median process 2/5 length of stalk, rounded or tapered
+terminally, proximal end opposed to tip of stalk and flattened obliquely;
+lateral processes 2/3 length of median process, deeper than wide, curved;
+tuberosities of stalk well developed, confluent medially, visible in
+dorsal view; in end-view dorsal concavity narrow, moderately deep,
+rounded, ventral concavity wide, deep, flattened; base wider ventrally
+than dorsally; shaft tapering more or less uniformly, terminally
+inflated.
+
+In the relative sizes, to each other and to the stalk, of the three
+digitate ossifications _M. oregoni_ resembles closely the Old World
+representative of the same subgenus, _M. (Chilotus) socialis_, as figured
+by Argyropulo (1933b:181). In _M. oregoni_ the greatest width of the
+baculum is more proximal on the stalk than in the _M. socialis_ figured
+by Argyropulo but closely resembles the baculum of the _M. socialis_
+figured by Didier (1954:242). In possessing a shallow emargination in the
+base of the stalk and in possessing a median process that is smaller than
+the lateral processes, _M. socialis_, as figured by Didier, differs from
+_M. oregoni_. The baculum figured by Argyropulo (_loc. cit._) of
+_Sumeriomys colchicus schidlovskii_ [ = _Microtus (Chilotus) socialis
+schidlovskii_ according to Ognev, 1950:392] differs from other _Chilotus_
+that have been studied in having an unusually elongate median process and
+a more distal placement of the widest part of the stalk.
+
+_Specimens examined_: Three, of the subspecies _M. oregoni oregoni_, from
+5 mi. N Orick, Humboldt Co., California, 3-C-248, collection of W. B.
+Quay; from Mary's Peak, Benton Co., Oregon, 66, collection of F. W.
+Sturges; and from Sec. 3, T. 11S, R. 5W, Benton Co., Oregon, 79183.
+
+
+Microtus (Stenocranius) gregalis (Pallas)
+
+Fig. 34
+
+Baculum: Length of stalk (2.4 mm.) 1-3/4, times greatest breadth, 4-1/3
+times greatest depth; median ossified process well developed, more than
+1/3 length of stalk, higher than wide, slightly bowed, closely appressed
+to terminus of shaft; basal tuberosities of stalk moderately developed,
+confluent medially, posterior profile of medial apex rounded in dorsal
+view, lateral indentations present, hence trilobate outline; in proximal
+end-view base wider ventrally, ventral concavity broader than dorsal
+concavity but of equal depth, medial constriction 2/3 greatest depth;
+shaft slender in distal part, inflated terminally, and wider than high at
+mid-point of stalk; lateral profile a smooth slope of gradually
+decreasing curvature from point of greatest width to near distal end.
+
+The baculum of this species figured by Ognev (1950:461) differs in having
+lateral ossified processes, and a more rounded base of the stalk.
+Resemblance to the New World _Stenocranius_ is discussed below.
+
+_Specimen examined_: One from "Eastern Europe," 8059.
+
+
+Microtus (Stenocranius) miurus Osgood
+
+Figs. 32 and 33
+
+Baculum: Length of stalk (2.8 mm.) 1-1/2 times greatest breadth, 3-1/2
+times greatest depth; median process ossified, 2/5 to 3/5 length of
+stalk, laterally compressed, sometimes arched in dorsoventral plane;
+lateral processes cartilaginous, slender; basal tuberosities well
+developed, averaging less enlarged than shown in Figure 32, but more
+angular in lateral outline than shown in Figure 33; tuberosities
+confluent posteriorly; posterior profile smoothly rounded to trilobate,
+curvature at point of greatest breadth usually acute; in proximal
+end-view base wider dorsally, deep dorsal concavity, shallow ventral
+concavity, medial constriction 3/5 of greatest depth; shaft slender
+anteriorly, at mid-point of stalk twice as wide as high, at tip higher
+than wide, laterally inflated; lateral profile in most specimens abruptly
+curved anterior to point of greatest breadth.
+
+The single specimen of the Old World _M. (Stenocranius) gregalis_
+examined resembles the New World _M. (Stenocranius) miurus_ in the
+angular lateral profile at the point of greatest breadth of the stalk,
+slender shaft in comparison to broad base of stalk, and presence of a
+single well-developed laterally compressed median process. The base of
+the stalk in the baculum of _M. gregalis_ is less well developed and
+smaller than in the baculum of _M. miurus_.
+
+_Specimens examined_: Nine, all of the subspecies _Microtus miurus
+muriei_, from the Brooks Range, Alaska; 51077 (Lake Schrader, 145°09'50",
+69°24'28", 2900 ft., Romanzof Mts.); 51151, 51152, 51154, 51164, 51166,
+51169 (last 6 from Wahoo Lake, 69°08', 146°58', 2350 ft.); 51210, 51213
+(last 2 from Porcupine Lake, 68°51'57", 146°29'50", 3140 ft.).
+
+
+Microtus (Chionomys) nivalis Martins
+
+Fig. 47
+
+Baculum: Greatest length of stalk (2.7 mm.) 2-1/4 times greatest breadth,
+4-1/2 times greatest depth; three digitate processes, lateral processes
+mostly cartilaginous in single adult examined; median process well
+ossified, approximately 1/3 length of stalk, basally notched, not arched,
+laterally compressed distally; base of stalk broad and flat, basal
+tuberosities well developed, separate; posterior profile in dorsal view
+rounded, convex except for medial notch separating tuberosities; dorsal
+and ventral concavities deep, broad, equal; medial constriction less than
+1/2 greatest depth; in dorsal view shaft tapering gradually from widest
+point, terminally rounded; at mid-point of stalk almost twice as wide as
+high.
+
+In the elongate, largely cartilaginous lateral processes of the baculum,
+the specimen described above resembles _M. longicaudus_. The size of the
+median process in comparison to the size of the stalk is also the same.
+The lateral processes have larger ossifications and the base of the stalk
+is more robust in _M. longicaudus_ than in _M. nivalis_.
+
+The well ossified lateral processes and enlarged base of Didier's
+(1954:240) specimen suggest that it is of a more mature individual than
+the one described above. These specimens of _M. nivalis_, as well as the
+specimens of _M. longicaudus_, exhibit dorso-ventral flattening of the
+mid-part of the base of the stalk.
+
+The baculum of a specimen from Switzerland is weakly developed, of small
+size (shaft 2.0 mm. in length), slender, thin, spatulate, and terminally
+inflated. Digital processes were not observed, perhaps owing to excessive
+maceration in preparation. The general appearance of the baculum is that
+of an immature individual, although the animal was not small (165 mm.
+total length in preservative).
+
+_Specimens examined_: Two _Microtus nivalis nivalis_; Zermatt, Valais,
+Switzerland, 67105; Wetterstein, Germany, 65127.
+
+
+Microtus (Chionomys) longicaudus (Merriam)
+
+Fig. 48
+
+Baculum: Base of stalk well developed, greatest length (3 mm.) 1-3/4
+times greatest breadth, 3-2/3 times greatest depth; three ossified
+processes; base of median process rounded; median process slightly curved
+in dorsoventral plane, in length almost 1/3 greatest length of stalk;
+ossifications in lateral processes variable in size, frequently widely
+separated from shaft by cartilage, rarely as large as median
+ossification; basal tuberosities usually well-developed, medially
+confluent; profile of base in dorsal view trilobate or irregularly convex
+throughout; constriction 1/2 greatest depth; shaft relatively straight or
+slightly bowed ventrally or dorsally, shaft at mid-point of stalk wider
+than high; tip of shaft laterally inflated; widest point of stalk
+approximately 1/4 length of stalk from proximal end; lateral profile in
+dorsal view tapers gradually onto shaft anteriorly from point of greatest
+width of stalk; shaft variable, from slender terminally and nearly
+parallel sided (Fig. 48), to broad distally and tapered.
+
+In many of the features that distinguish _M. longicaudus_ (and the
+closely related insular species _M. coronarius_) from other North
+American _Microtus_, _longicaudus_ resembles the Old World species of the
+subgenus _Chionomys_ (that is to say, _M. nivalis_, _M. gud_, and _M.
+roberti_). These features are medium size, long tail, grayish color,
+montane habitat, relatively short molar tooth-row, moderate sized and
+unconstricted incisive foramen, relatively decurved upper incisors,
+elongate nasals, relatively broad interorbital region without
+well-developed median ridge, and similar chromosomes (Matthey, 1955:178).
+For these reasons I am here referring _Microtus longicaudus_ to the
+subgenus _Chionomys_; previously it has not been referred to that
+subgenus.
+
+_Specimens examined_: Six, of three subspecies; _Microtus longicaudus
+littoralis_, Sullivan Island, Alaska, 42972, 42969; _M. l. mordax_, 3/4
+mi. N, 2 mi. W Allenspark, 8400 ft., Boulder Co., Colorado, 50335, 76829;
+_M. l. sierrae_, Crane Flat, Mariposa Co., California, 50252, 50253.
+
+
+Microtus arvalis (Pallas)
+
+Fig. 22
+
+Baculum: In the single specimen examined, stalk small, greatest length
+(2.3 mm.) 2-1/3 times greatest width, almost 6 times greatest depth,
+flattened proximally; three well-developed digitate processes, the median
+one ossified, the lateral processes cartilaginous; median ossification
+laterally compressed and decurved at tip, bilobate at base; basal
+tuberosities of stalk weakly developed, medially confluent; posterior
+profile in dorsal view evenly rounded; ventral concavity deeper and
+narrower than dorsal concavity, but both comparatively shallow; medial
+constriction 2/3 greatest depth; shaft straight, at mid-point twice as
+wide as deep; lateral profile tapering from greatest width gradually to
+parallel sides of distal third of stalk.
+
+From the baculum of _Microtus arvalis_ figured by Ognev (1950:173), and
+from the baculum figured by Didier (1954:238) my specimen differs in the
+absence of lateral ossifications in the digitate processes, smaller and
+slenderer median ossification, and weaker base. These differences in part
+may be owing to a difference in age, my specimen being the less mature.
+
+_Specimen examined_: One from Vidy, Switzerland, 67101.
+
+
+Microtus orcadensis Millais
+
+Fig. 24
+
+Baculum: In the one specimen examined, stalk broad, greatest length (2.6
+mm.) 1-1/2 times greatest breadth, 3-1/2 times greatest depth; three
+digitate processes ossified; median process relatively broad, in length
+more than 1/2 length of stalk, triangular in dorsal view, with small
+spurs posterolaterally, middorsal ridge posteriorly; lateral
+ossifications slightly curved, slenderer, less than 1/2 depth and less
+than 1/2 transverse thickness of median process; basal tuberosities
+well-developed, confluent medially; in end-view base wider dorsally than
+ventrally, dorsal concavity broader and more abruptly curved at mid-point
+than ventral concavity; constriction 1/2 greatest depth; posterior
+profile in dorsal view notched, setting off a posterior shelf; stalk
+including shaft wider than deep throughout, at mid-point width twice
+depth; lateral profile abruptly curved anterior to point of greatest
+width, sides of shaft tapering gradually anteriorly to rounded uninflated
+tip.
+
+The baculum of this insular species, placed in the "_arvalis_" group by
+Ellerman (1941:595), resembles the baculum of both _Microtus agrestis_
+and _Microtus guentheri_ more than it resembles the baculum of _Microtus
+arvalis_. Similarities in the chromosomes of _M. arvalis_ and _M.
+orcadensis_ were noted by Matthey (1953:254, 279), who was of the opinion
+that _M. orcadensis_ is an insular derivative of the _arvalis_-group.
+
+_Specimen examined_: One from the Orkney Islands, 67106.
+
+
+Microtus guentheri Danford and Alston
+
+Fig. 23
+
+Baculum: In the one specimen examined, stalk broad, greatest length (2.9
+mm.) 1-1/2 times greatest breadth, 3-1/2 times greatest depth; three
+digitate processes ossified; median process slightly less than 1/2 length
+of stalk, broad, dorsally curved; curved lateral ossifications shorter
+and more slender than median ossification; basal tuberosities well
+developed, angular, confluent across posterior border of projecting
+shelf; in end-view tuberosities projecting ventrolaterally from central
+shelf; dorsal surface at medial constriction flat, ventral surface
+broadly and deeply concave; posterior profile in dorsal view trilobate,
+central lobe formed by posteriorly flattened shelf, surface of attachment
+visible only on lateral lobes; at mid-point stalk almost twice as wide as
+deep, depth of shaft greater than width proximal to inflated terminus.
+
+_Specimen examined_: One from Palestine, 67104.
+
+
+Microtus fortis Büchner
+
+Fig. 25
+
+Baculum: Stalk large, greatest length (3.8 mm.) 1-4/5 times greatest
+breadth, 4-1/2 times greatest depth; three digitate processes ossified;
+median ossification almost 1/3 length of stalk; lateral ossifications
+slender, smaller than median ossification; posterior profile of stalk in
+dorsal view trilobate, basal tuberosities well developed, confluent
+medially; in end-view dorsal concavity broader and deeper than ventral
+concavity; medial constriction pronounced (less than 1/2 greatest depth);
+lateral profile at widest point of stalk convex, becoming abruptly
+concave as the flange of the basal tuberosities grades into the shaft,
+then gradually converging to narrowest point 1/3 of length of stalk from
+the terminus; stalk wider than deep in proximal 2/3, circular in cross
+section in terminal 1/3, slight terminal inflation.
+
+A specimen figured by Ognev (1950:297) has the same general proportions,
+slender lateral processes, and proximal placement of the point of
+greatest breadth.
+
+_Specimens examined_: Two from Chipo-ri, Korea, 60443, 63841.
+
+
+Microtus montanus (Peale)
+
+Figs. 19, 20 and 21
+
+Baculum: Stalk broad, greatest length (varying with subspecies from 2.3
+to 3.1 mm.) 1-1/2 to 1-3/4 times greatest breadth, 3-1/3 to 4-1/3 times
+greatest depth; three ossified processes, median one largest, more than
+twice as wide and as deep as shorter, slenderer, lateral processes;
+median process laterally compressed distally except in one specimen in
+which moderately inflated distally, proximally enlarged in some specimens
+(Fig. 21) and 1/3 to 2/5 length of stalk; base broad, posterior profile
+in dorsal view evenly convex throughout, at widest point of stalk
+abruptly incurved; basal tuberosities moderately to strongly developed,
+medially confluent; in end-view base wider ventrally than dorsally,
+dorsal concavity slightly to much deeper than the nearly flattened
+ventral concavity; medial constriction 2/3 to 4/5 of greatest depth;
+shaft relatively slender, at mid-point of stalk slightly wider than high
+and 1/4 as wide as base of stalk, terminally rounded or slightly
+inflated; lateral profile in dorsal view a gradual curve from point of
+greatest width anteriorly onto shaft.
+
+The different subspecies figured show the essential characteristics of
+the species, differing primarily in size.
+
+_Specimens examined_: Fourteen, of three subspecies; _Microtus montanus
+amosus_, 1/2 mi. E Soldier Summit, Wasatch Co., Utah, 62241; _M. montanus
+fusus_, La Manga Pass, Conejos Co., Colorado, 42164; 5 mi. N, 26 mi. W
+Saguache, 9500 ft., Saguache Co., Colorado, 42307, 42315; 5 mi. N, 27 mi.
+W Saguache, 9350 ft., Saguache Co., Colorado, 42308; 5 mi. N, 28 mi. W
+Saguache, 9325 ft., Saguache Co., Colorado, 42309; 5 mi. S, 24 mi. W
+Antonito, 9600 ft., Conejos Co., Colorado, 42327, 42330; Prater Canyon,
+Mesa Verde National Park, Montezuma Co., Colorado, 69456, 69457, 69463;
+_Microtus montanus nanus_, 2 mi. N, 2 mi. W Pocatello, Bannock Co.,
+Idaho, 57470, 57472; 3/4 mi. N, 2 mi. W Allenspark, 8400 ft., Boulder
+Co., Colorado, 50330.
+
+
+Microtus townsendii (Bachman)
+
+Fig. 41
+
+Baculum: Stalk broad, greatest length (3.0 mm.) 1-1/2 times greatest
+breadth, 4-1/2 times greatest depth; three ossified processes, median one
+largest, deeper and more than twice as wide as curved, shorter,
+compressed lateral processes and more than 2/5 as long as stalk; base
+broad, in dorsal view posterior profile trilobate, basal tuberosities
+visible; basal tuberosities well developed, medially confluent; in
+end-view base wider ventrally than dorsally, dorsal concavity deeper than
+ventral concavity; medial constriction 3/5 of greatest depth; shaft
+broad, at mid-point more than twice as wide as high and 1/3 as wide as
+base of stalk, terminally rounded.
+
+_Specimens examined_: Three, all _M. t. townsendii_; Fort Lewis, Pierce
+Co., Washington, 57998, subadult; Sec. 33, T. 11S, R. 5W, Benton Co.,
+Oregon, 79186; Sec. 5, T. 12S, R. 4W, Benton Co., Oregon, 79188.
+
+
+Microtus oeconomus (Pallas)
+
+Fig. 44
+
+Baculum: Stalk broad and flattened, greatest length (3.5 mm.) 1-2/3 to 2
+times greatest width, 4 to 5-1/2 times greatest depth; three ossified
+processes, median one largest, lateral processes slender, relatively
+small; length of median process 3/8 length of stalk; median process
+decurved, dorsoventrally flattened in some specimens, widened at base;
+attachment of processes to shaft displaced ventrally; base of stalk
+widened, posterior profile in dorsal view usually trilobate, in a few
+cases rounded, median lobe forming posterior shelf, lateral lobes
+dorsally raised and forming margins of lateral tuberosities; in end-view
+thickness frequently more or less uniform throughout central part, broad
+depression dorsally, ventral concavity narrower and shallower (as
+figured); base, and occasionally shaft, flattened, width at mid-point of
+stalk 2 to 3 times depth, narrowest point posterior to terminal inflation
+of shaft in terminal 1/3 of shaft.
+
+The baculum of _M. oeconomus_ (Old World) figured by Ognev (1950:257)
+resembles but exceeds that of _M. oeconomus_ (New World) in the
+relatively large median process and slender lateral processes, but
+differs noticeably in the presence of a deep median notch in the base of
+the stalk. A specimen from Hungary is intermediate between Ognev's
+specimen and those from the New World in both size of median process and
+size of lateral processes, and has an unnotched base resembling that in
+Figure 44.
+
+_Specimens examined_: Ten, of three subspecies; _M. oeconomus gilmorei_,
+Umiat, Alaska, 51354, 51361, 51399, 51408; Lake Schrader, Brooks Range,
+Alaska, 51422; _M. o. macfarlani_, 5 mi. NNE Gulkana, Alaska, 43039,
+43041; 20 mi. NE Anchorage, Alaska, 43044; Kelsall Lake, British
+Columbia, 43048; _M. o. mehelyi_, Kisbalatan, Hungary, 75159.
+
+
+Microtus mexicanus (Saussure)
+
+Figs. 35 and 36
+
+Baculum: Stalk attenuate, greatest breadth relatively near proximal end;
+greatest length (3.1 to 3.4 mm.) more or less twice greatest breadth, 4
+to 5 times greatest depth; usually a single process ossified; lateral
+processes relatively small, cartilaginous or (in three specimens, 63094,
+69453, 68019) with small ossifications; median process relatively small,
+sometimes appressed to tip of shaft, in length less than 1/4 length of
+stalk; posterior profile in dorsal view rounded, flattened posteriorly,
+or in some specimens trilobate with angular edges; in end-view relative
+depths of dorsal and ventral concavities variable, dorsal usually deeper
+than ventral; distal end of stalk frequently bowed dorsally; shaft
+slender distally, sometimes slightly inflated terminally, or (in one
+specimen, 63085) near tip small lateral projections that are perhaps
+fused lateral ossifications; lateral profile in dorsal view a gradual
+slope anteriorly from point of greatest width to slender tip.
+
+_Specimens examined_: Thirteen, of four subspecies; _Microtus mexicanus
+mexicanus_, Las Vigas, Veracruz, 30692; Nevada de Toluca, México, 63101;
+Valle de Bravo, México, 63094; _Microtus mexicanus mogollonensis_, Mt.
+Taylor, Valencia Co., New Mexico, 63298, 76830; Park Well, Mesa Verde
+National Park, Montezuma Co., Colorado, 69448, 69453; Upper Nutria,
+McKinley Co., New Mexico, 69997, 70000; _Microtus mexicanus phaeus_,
+Sierra Patamba, 9000 ft., Michoacán, 63085; _Microtus mexicanus
+subsimus_, 2 mi. E Mesa de Tablas, Coahuila, 58916; 13 mi. E San Antonio
+de las Alazanas, Coahuila, 68019, 68021.
+
+
+Microtus californicus (Peale)
+
+Fig. 37
+
+Baculum: Stalk elongate, greatest length (3.0 mm.) 2-1/3 times greatest
+breadth, 4-1/2 times greatest depth; median process ossified, 1/4 length
+of stalk, basally broadened, flattened and shallowly grooved ventrally to
+fit tip of shaft, to which the process is closely appressed; lateral
+processes cartilaginous; ends of stalk bowed upwardly; posterior profile
+of base of stalk rounded or slightly trilobate if posterolateral
+concavities form in tuberosities; moderate development of tuberosities,
+in end-view dorsal concavity slightly deeper and narrower than ventral
+concavity, both comparatively shallow, median constriction 4/5 greatest
+depth; shaft curved, more or less terete at mid-point of stalk,
+terminally inflated dorsally; lateral profile in dorsal view gradually
+curved from point of greatest width anteriorly onto shaft.
+
+_Specimens examined_: Two, of two subspecies; _Microtus californicus
+californicus_, 1 mi. NE Berkeley, in Contra Costa Co., California, 76828;
+_Microtus californicus mohavensis_, 1/2 mi. SE Victorville, San
+Bernardino Co., California, 63745.
+
+
+Microtus pennsylvanicus (Ord)
+
+Figs. 14, 15, 16 and 17
+
+Baculum: Stalk heavy, broad, greatest length (2.2 to 3.0 mm.) 1-1/3 to
+1-2/3 times greatest breadth, up to 3-3/4 times greatest depth; three
+ossified processes, median one largest, usually not twice so deep as
+lateral ossifications; median process usually distinctly widened basally,
+in length approximately 1/2 length of stalk; base broad, frequently
+angular laterally and basally, sometimes bilobate; basal tuberosities
+well developed, medially confluent; in end-view more or less uniformly
+biconvex or ventral surface more flattened than dorsal surface, medial
+constriction 1/2 to 2/3 greatest depth; shaft relatively heavy, at
+mid-point stalk almost twice as wide as deep and 1/3 as wide as base of
+stalk; shaft terminally rounded and sometimes slightly inflated; lateral
+profile in dorsal view abruptly or gradually curved anterior to point of
+greatest width and then gradually curved anteriorly.
+
+Specimens examined averaged slightly smaller and were more variable than
+those described by Hamilton (1946:382). The greater variation may be in
+part geographic, as five subspecies are represented. Lateral processes
+are the last to ossify. One specimen (75082) with well-ossified median
+process lacks any lateral ossification. Four bacula of _M.
+pennsylvanicus_ (locality not specified) studied by Dearden (1958:547)
+agree in general with the description above.
+
+One specimen shows a break, perhaps resulting from injury, in the shaft
+(Fig. 14). One specimen has a posteromedian spine on the median digital
+ossification (Fig. 16). Comparison with _M. agrestis_ is included with
+the description of _M. agrestis_.
+
+_Specimens examined_: Thirteen, of six subspecies; _Microtus
+pennsylvanicus alcorni_, 20 mi. NE Anchorage, Alaska, 43043; _Microtus
+pennsylvanicus finitus_, Laird, Yuma Co., Colorado, 68544; _Microtus
+pennsylvanicus modestus_, 5 mi. N, 26 mi. W Saguache, 9500 ft., Saguache
+Co., Colorado, 42306; 3 mi. N, 16 mi. W Saguache, 8500 ft., Saguache Co.,
+Colorado, 42416, 42417, 42418; 1 mi. S, 2 mi. E Eagle Nest, 8100 ft.,
+Colfax Co., New Mexico, 42430, 42439; _Microtus pennsylvanicus
+pennsylvanicus_, 2 mi. S, 3 mi. E Ft. Thompson, 1370 ft., Buffalo Co.,
+South Dakota, 42379; Vermillion, Clay Co., South Dakota, 37070; _Microtus
+pennsylvanicus pullatus_, 12 mi. S, 5 mi. E Butte, Silver Bow Co.,
+Montana, 57501, 57503; _Microtus pennsylvanicus uligocola_, Muir Springs,
+2 mi. N, 2-1/2 mi. W Ft. Morgan, Morgan Co., Colorado, 75082.
+
+
+Microtus agrestis (Linnaeus)
+
+Fig. 18
+
+Baculum: Greatest length of stalk (2.9 mm.) twice greatest breadth, 4-1/2
+times greatest depth; stalk well developed, shaft not flattened
+dorsoventrally; large median ossified process, minute lateral
+ossifications in single specimen examined; length of stalk 2-1/2 times
+length of median ossification which is higher than wide, slightly
+decurved, sagittate in dorsal view, with three-cornered base; basal
+tuberosities of stalk moderately well developed, medially joined;
+posterior profile in dorsal view evenly rounded; ventral concavity
+broader than, but of comparable depth to, dorsal concavity in end-view,
+base of stalk wider ventrally, constriction 3/4 greatest depth; at
+mid-point of stalk shaft is but slightly wider than high; pronounced
+terminal inflation of shaft; lateral profile in dorsal view sloping
+abruptly from widest point of stalk anteriorly onto stalk which then
+tapers more gradually to terminal inflation.
+
+From the baculum of its New World counterpart, namely _Microtus
+pennsylvanicus_, my specimen of _Microtus agrestis_ and the specimen
+figured by Didier (1954:239) differ in their minute lateral processes,
+relatively larger median processes, and more elongate, less
+dorsoventrally flattened shafts.
+
+The specimen of _M. agrestis_ figured by Ognev (1950:320), in dorsal view
+has lateral concavities producing a somewhat trilobate outline in the
+base of the stalk, and the lateral processes are well developed; the
+median process is larger and bulbous, wider distally than proximally.
+Without larger numbers of bacula of _M. agrestis_ I am unable to
+reconcile these differences. The differences between _M. agrestis_ and
+_M. pennsylvanicus_ seem comparable to the differences between some other
+species of _Microtus_.
+
+_Specimen examined_: One, from Gryon, Switzerland, 67102.
+
+
+Microtus (Pedomys) ochrogaster (Wagner)
+
+Fig. 31
+
+Baculum: Stalk broad, greatest length (3.2-4.0 mm.) 1-2/3 to 2 times
+greatest breadth, 2-1/2 to 4 times greatest depth; median process
+ossified, relatively small, less than 3/10 length of stalk; lateral
+processes arising from subterminal part of stalk, cartilaginous or with
+small ossifications; posterior profile in dorsal view broadly rounded or
+slightly angular, widest point of stalk 1/6 to 1/4 the length of stalk
+from base; basal tuberosities well developed and medially confluent, in
+end-view dorsally convex, or at least less deeply concave than ventrally;
+shaft straight, base bent ventrally or more commonly dorsally; at
+mid-point of stalk wider than high, often twice as wide as high; viewed
+from above, lateral profile from point of greatest breadth to middle of
+shaft a gradual sigmoid curve; slight terminal inflation of shaft.
+
+_Specimens examined_: Forty-one, of three subspecies; _Microtus
+ochrogaster haydeni_, Muir Springs, 2 mi. N, 2-1/2 mi. W Ft. Morgan,
+Morgan Co., Colorado, 74995, 74998, 74999, 75002; 1 mi. W Laird, Yuma
+Co., Colorado, 57304, 76833; 2 mi. N, 2 mi. W Haigler, Dundy Co.,
+Nebraska, 75016; 2 mi. S Franklin, Franklin Co., Nebraska, 75043, 75044;
+Atwood, Rawlins Co., Kansas, 75020, 75023, 75025, 75027, 75028; 1 mi. N,
+2 mi. E Oberlin, Decatur Co., Kansas, 75030, 75032, 75034, 75035, 75036;
+1-1/2 mi. N, 1/4 mi. E Norton, Norton Co., Kansas, 68327; 1 mi. SW
+Norton, Norton Co., Kansas, 75037; 2 mi. S, 1 mi. W Norton, Norton Co.,
+Kansas, 75038; _M. ochrogaster ochrogaster_, Rydal, Republic Co., Kansas,
+75047-75053, 75060, 75062, 75063, 75066, 75070, 75071, 75073; 1 mi. N, 1
+mi. W Holton, Jackson Co., Kansas, 75077; 2 mi. W Court House, Lawrence,
+Douglas Co., Kansas, 76832; Univ. Kansas Natural History Reservation,
+Douglas Co., Kansas, 68536; _M. ochrogaster taylori_, Meade County State
+Park, Kansas, 68539, 68542.
+
+
+Microtus (Pitymys) pinetorum (LeConte)
+
+Figs. 27 and 28
+
+Baculum: Stalk broad, greatest length (2.5 to 2.7 mm.) 1-2/3 times
+greatest breadth, 4 times greatest depth; median process ossified, size
+small, 1/5 length of stalk, higher than wide, having small anterodorsal
+prominence in both specimens examined; lateral processes cartilaginous,
+relatively small, displaced posteriorly, attenuate; posterior margin in
+dorsal view broadly rounded, or having blunt median apex, convex
+throughout; basal tuberosities moderately well developed, medially
+confluent, barely visible in dorsal view when mature; in end-view median
+constriction 4/5 greatest depth, ventral concavity deeper than dorsal
+concavity, both comparatively shallow; stalk at mid-point 1-1/2 times as
+wide as deep; shaft relatively slender, bowed dorsally at tip, relatively
+straight otherwise; lateral profile in dorsal view a gradual concave
+slope from point of greatest width anteriorly to distal part of shaft.
+
+_Specimens examined_: Two, from Douglas Co., Kansas, 76834 (2 mi. N
+Baldwin), 68545 (1 mi. NE Pleasant Grove).
+
+
+Microtus (Pitymys) parvulus (Howell)
+
+Fig. 40
+
+Baculum: Stalk broad, greatest length (2.4 mm. in specimen examined)
+1-3/4 times greatest breadth, 4 times greatest depth; median process
+ossified, size small, less than 1/4 length of stalk, wider than high,
+terminally flattened; lateral processes cartilaginous, relatively small,
+attenuate; posterior margin in dorsal view flattened, irregularly curved
+with concavities medially and laterally; basal tuberosities well
+developed, medially confluent; visible in dorsal view; in end-view median
+constriction 2/3 greatest depth, ventral concavity well-formed, no dorsal
+concavity; stalk at mid-point twice as wide as deep; shaft relatively
+slender, bowed dorsally toward tip; in dorsal view lateral profile a
+gradual concave slope from point of greatest width anteriorly to distal
+part of shaft; tip of shaft enlarged.
+
+The baculum of _M. parvulus_ resembles that of _M. pinetorum_ more than
+it resembles the baculum of any other microtine studied, differing
+primarily in smaller size.
+
+_Specimen examined_: One, from 1 mi. W Micanopy, Alachua Co., Florida,
+Univ. Florida No. 1508.
+
+
+Microtus (Pitymys) quasiater (Coues)
+
+Figs. 29 and 30
+
+Baculum: Stalk broad, greatest length (2.6-3.2 mm.) 1-1/3 to 1-2/3 times
+greatest breadth, 3-1/3 to 3-2/3 times greatest depth; median process
+ossified, with ventral depression, process 1/4 to 1/3 length of stalk,
+appressed to tip of shaft, wider than high proximally, relatively broad
+terminally; lateral processes cartilaginous, small, attenuate; posterior
+profile of stalk in dorsal view broadly rounded, bilobate, or trilobate,
+median lobe formed by posterior projection of dorsal shelf between
+enlarged lateral tuberosities that form outer lobes, posterolateral faces
+of these tuberosities visible in dorsal view of stalk; in end-view dorsal
+surface slightly concave, ventral concavity broad and deep, median
+constriction 1/2 greatest depth; shaft flattened except tip that is more
+terete, and bowed dorsally; at mid-point, stalk twice as wide as high;
+shaft relatively slender terminally, narrower than median ossification.
+
+The baculum of _M. quasiater_ is the largest and has the best developed
+base and median process of the three American species of the subgenus
+_Pitymys_. The three species closely resemble each other in basic form.
+
+_Specimens examined_: Five, all from Veracruz; Teocelo, 4500 ft., 30709,
+30711; 4 km. N Tlapacoyán, 1700 ft., 24466; 5 km. N Jalapa, 4500 ft.,
+19869, 19878.
+
+
+Microtus (Pitymys) fatioi (Mottaz)
+
+Fig. 26
+
+The baculum of a single specimen (KU 67103) of _M. fatioi_ from Zermatt,
+Valais, Switzerland, was examined. The baculum is immature, as evidenced
+by its small size, slender stalk and absence of ossified processes,
+therefore no characterization is included.
+
+The baculum of another Old World species of the subgenus _Pitymys_, _M.
+pyrenaicus_ from France, figured and described by Didier (1954:242-243),
+differs from all New World _Pitymys_ examined in processing ossified
+lateral processes.
+
+The status of _Pitymys_, as a genus or as a subgenus, is uncertain. Hall
+and Cockrum (1953:448) considered the North American _Pitymys_ and
+_Pedomys_ as subgenera of _Microtus_. They did not state specifically the
+basis for this point of view, but mention the fact that these two
+subgenera (_Pitymys_ and _Pedomys_) closely resemble each other
+cranially. These authors did not study nor comment upon the status of the
+Old World _Pitymys_. It may be asked whether the Old World and New World
+_Pitymys_ have developed as fossorial _Microtus_ independently, or from
+an ancestor common to both groups and not common to any other _Microtus_.
+Matthey (1955:202) found 62 chromosomes (2N) in both the New World
+_Pitymys pinetorum_ and the Old World _Pitymys duodecimcostatus_. This
+suggests, but does not prove, common ancestry.
+
+
+Neofiber alleni True
+
+Fig. 49
+
+Baculum: Stalk massive, greatest length (4.7 mm.) 1-3/4 times greatest
+breadth, 4 times greatest depth; ossification in digitate processes
+variable; in one (KU 27123) of two specimens examined lateral processes
+ossified and median process unossified, as in two specimens examined by
+Hamilton (1946:379) from "southern Florida"; in my other specimen (KU
+27268) that is possibly more mature, median process ossified although
+less deeply stained than lateral ossifications or stalk; posterior
+profile in probable dorsal view roughly rounded; in end-view probable
+dorsal concavity deep, ventral concavity broad but shallow, and with
+center convex; median constriction 3/5 greatest depth; shaft heavy, least
+depth 2/3 greatest depth of base; stalk, at mid-point, slightly wider
+than deep and more than 1/3 width of base; lateral profile in dorsal view
+sharply incurved distal to point of greatest breadth, shaft therefore
+relatively distinct from basal part of stalk; slight subterminal
+constriction; tip less reduced in the two specimens examined than in two
+figured by Hamilton. In preparation, the tissues that make it possible to
+distinguish with certainty the dorsal and ventral surfaces of the baculum
+were removed in both specimens.
+
+_Specimens examined_: Two, of the subspecies _Neofiber alleni alleni_, 2
+mi. S Gainesville, Alachua Co., Florida, 27268; 1 mi. E Courtenay,
+Merritt Island, Brevard Co., Florida, 27123.
+
+
+Lagurus curtatus (Cope)
+
+Fig. 46
+
+Baculum: Stalk slender, greatest length (2.5 mm.) 2 to 2-2/3 times
+greatest breadth, 4 to 5 times greatest depth; three ossified processes;
+median one more than 1/3 length of stalk, curved dorsally toward tip,
+proximally flattened and having acute lateral angles in dorsal view,
+wider than deep except in distal half; lateral processes smaller than
+median one, slenderer, shorter, of approximately same depth, also curved
+dorsally; base of stalk well developed, basal tuberosities medially
+confluent, in part visible in dorsal view, in end-view wider ventrally
+than dorsally, dorsal and ventral concavities of equal depth and both
+wide, medial constriction 1/2 greatest depth; posterior profile in dorsal
+view broadly bilobate; lateral profile with abrupt transition from basal
+tuberosities to gradually converging, slightly curved sides of shaft;
+shaft terminally inflated.
+
+Dearden (1958:543) described and figured the bacula of six subspecies of
+_Lagurus curtatus_ and two Asiatic species, _Lagurus lagurus_ and
+_Lagurus luteus_. He examined at least 34 specimens of _L. curtatus_ and
+found geographic variation in size, breadth of shaft distally, and
+proportions of digital ossifications to each other and to the stalk. The
+description that I have given above pertains to _L. c. levidensis_.
+
+The baculum of the Asiatic _Lagurus (Lagurus) lagurus_ figured by Ognev
+(1950:554) agrees with that of _Lagurus (Lemmiscus) curtatus_, described
+here, in the relatively elongate shaft and slender stalk, the proportions
+of the processes, and the well-formed and moderately enlarged base of the
+stalk. The bacula of three _Lagurus lagurus_ examined by Dearden
+(1958:545) were of older individuals than the specimen that Ognev figures
+and differ from it and from bacula of _Lagurus curtatus_ (all subspecies)
+in the unusual, almost heart shaped, median process, and in larger size.
+_Lagurus luteus_ examined by Dearden (1958:545) differs from both
+_Lagurus lagurus_ and _Lagurus curtatus_ in lacking lateral digital
+ossifications and in having shorter median digital ossifications and
+wider base of stalk.
+
+_Specimens examined_: Seven _Lagurus curtatus levidensis_ from Wyoming; 9
+mi. S Robertson, Uinta Co., 26045, 26053; 8 mi. S, 2-1/2 mi. E Robertson,
+Uinta Co., 26049; Farson, Sweetwater Co., 37906; 16 mi. S, 11 mi. W
+Waltman, Natrona Co., 42457; 32 mi. S, 22 mi. E Rock Springs, 42465,
+42466.
+
+The following key to the bacula in some adult North American Microtinae
+is intended to help point out some of the most important differences. It
+should be noted that not all species can be keyed out on the basis of the
+baculum. The most difficult group in this respect includes the species of
+_Microtus_ that have small or no ossified lateral processes, especially
+species of the subgenera _Pedomys_ and _Pitymys_, and the two species
+_Microtus californicus_ and _Microtus mexicanus_ of the subgenus
+_Microtus_. Another complicating factor is the variability of bacula
+evident in some species even in the small samples available. It is to be
+expected that additional specimens will show variations not yet observed.
+
+
+KEY TO THE BACULA OF SOME NORTH AMERICAN MICROTINES
+
+  1. Length of lateral digital ossifications more than 1/3 breadth
+  of stalk                                                              2
+
+  1´. Length of lateral digital ossifications less than 1/3 breadth
+   of stalk or absent                                                  15
+
+  2. Size small (total length of baculum less than 5.5 mm.)             3
+
+  2´. Size large (total length of baculum more than 5.5 mm.)           14
+
+  3. Width at mid-point of stalk more than 1/3 greatest breadth of
+  stalk                                                                 4
+
+  3´. Width at mid-point of stalk less than 1/3 greatest breadth of
+  stalk,                                                                8
+
+  4. Stalk, viewed from proximal end hour-glass shaped, and width
+  of stalk less than 1/2 length of stalk.... _Phenacomys
+  intermedius_,                                                    p. 197
+
+  4´. Stalk not both hour-glass shaped when viewed from proximal
+  end, and with width less than 1/2 length of stalk                     5
+
+  5. Shaft thin basally, thickness less than 1/3 of greatest breadth    6
+
+  5´. Shaft thick basally, thickness 1/3 or more of greatest breadth    7
+
+  6. Stalk more or less straight, base not deflected. _Microtus
+  oeconomus_,                                                      p. 204
+
+  6´. Stalk spatulate, and base deflected from axis of shaft....
+  _Microtus guatemalensis_,                                        p. 198
+
+  7. Base enlarged, depth nearly 1/2 of breadth.... _Lemmus
+  trimucronatus_,                                                  p. 193
+
+  7´. Base moderately enlarged, depth near 1/3 of breadth....
+  _Microtus pennsylvanicus_, p. 206, or _Microtus townsendii_,     p. 204
+
+  8. Base hour-glass shaped as viewed from proximal end....
+  _Phenacomys intermedius_,                                        p. 197
+
+  8´. Not so                                                            9
+
+  9. Lateral processes separated from tip of shaft by more than the
+  thickness of the lateral process                                     10
+
+  9´. Lateral processes separated from tip of shaft by less than the
+  thickness of the lateral process                                     11
+
+  10. Lateral processes more than 1/2 the width of median
+  process.... _Microtus longicaudus_,                              p. 201
+
+  10´. Lateral processes slender, less than 1/2 the width of median
+  process.... _Microtus montanus_,                                 p. 204
+
+  11. Lateral ossifications equal in length to median
+  ossification.... _Clethrionomys_,                                p. 194
+
+  11´. Lateral ossifications shorter than median ossification          12
+
+  12. Size small, less than 3.4 mm. in total length....
+  _Microtus oregoni_,                                              p. 199
+
+  12´. Size medium, more than 3.4 mm. in total length                  13
+
+  13. Greatest width of stalk at a point about 1/3 of length of
+  stalk from base.... _Microtus chrotorrhinus_ (Hamilton, 1946:382).
+
+  13´. Greatest width of stalk at a point less than 1/3 of length of
+  stalk from base.... _Lagurus curtatus_,                          p. 210
+
+  14. Size of baculum larger, base more than 3 mm. wide, processes
+  all well developed.... _Ondatra zibethicus_,                     p. 198
+
+  14´. Size of baculum smaller, base less than 3 mm. wide, processes
+  poorly developed in some animals.... _Neofiber alleni_,          p. 209
+
+  15. At least one digital ossification present                        16
+
+  15´. Digital ossifications not present.... _Dicrostonyx
+  groenlandicus_,                                                  p. 193
+
+  16. Breadth of stalk at least 1/2 length of stalk                    17
+
+  16´. Breadth of stalk less than 1/2 length of stalk                  19
+
+  17. Length of stalk greater than 3.6 mm. and less than 1-1/2
+  times its greatest breadth.... _Microtus richardsoni_,           p. 199
+
+  17´. Length of stalk usually less than 3.6 mm., or if more than
+  3.6 mm. (up to 4.0 mm.) then length 1-1/2 times or more its
+  greatest breadth                                                     18
+
+  18. Median process attenuate distally in dorsal view, and
+  relatively long (more than twice its own breadth), 1/5 to 3/5 the
+  length of stalk; breadth of stalk usually 2/3 or more length of
+  stalk.... _Microtus miurus_,                                     p. 200
+
+  18´. Median process relatively blunt distally in dorsal view,
+  relatively short (usually less than 1/4 length of stalk), breadth
+  of stalk usually less than 2/3 length of stalk....
+  _Pitymys_, p. 208, _Pedomys_, p. 207, or _Microtus mexicanus_,   p. 205
+
+  19. Distal processes small and firmly ankylosed to distal end of
+  shaft.... _Phenacomys longicaudus_,                              p. 197
+
+  19´. Distal processes if present not firmly ankylosed to distal
+  end of shaft                                                         20
+
+  20. Dorsal concavity of base as viewed from proximal end usually
+  deeper than ventral concavity.... _Microtus mexicanus_,          p. 205
+
+  20´. Dorsal and ventral concavities of base equal in depth or
+  ventral one the deeper                                               21
+
+  21. Total length of baculum more than 3.6 mm.... _Microtus
+  californicus_,                                                   p. 205
+
+  21´. Total length of baculum less than 3.6 mm.... _Synaptomys
+  cooperi_,                                                        p. 194
+
+
+
+
+DISCUSSION
+
+
+Owing to shortness of lower incisors and present geographic distribution
+of the species, Hinton (1926:35) considered the Tribe Lemmi (lemmings) to
+be more primitive than the Tribe Microti (voles). The surviving lemmings
+are specialized in many features and therefore are considered as advanced
+end-products of an evolutionary radiation of a primitive microtine stock,
+of which all earlier stages are extinct.
+
+Hinton regarded _Dicrostonyx_ as the most primitive of the genera of
+lemmings on account of its more complex molar teeth (complexity was
+considered to be primitive), and on account of the presence of three
+primitive longitudinal rows of tubercles in unworn molars. The other
+three genera were arranged in order of increasing specialization as
+follows: _Synaptomys_, _Myopus_, _Lemmus_.
+
+If the baculum tended to retain its primitive character while
+specializations in the external anatomy developed, and if the above
+arrangement is correct the most primitive bacula would be found in
+_Dicrostonyx_ and in _Synaptomys_. The baculum in these two genera in
+comparison to that in _Myopus_ (as figured by Ognev, 1948:512) and
+_Lemmus_ has a slenderer stalk and smaller digital ossifications or none
+at all. The baculum in the genera of lemmings increases in robustness and
+the development of processes from _Dicrostonyx_, to _Synaptomys_, to
+_Myopus_, to _Lemmus_--the same order outlined above for total of
+specialization. The two extremes in this series are near the extremes of
+variation in bacula to be found in all microtines. The baculum in
+lemmings as a group cannot then be considered more primitive than in
+voles as a group, although the voles are usually considered to be more
+advanced. The situation in the voles, as we shall see, casts a different
+light on the matter.
+
+The voles, Tribe Microti, were considered by Hinton (1926:40) to be more
+advanced than the lemmings because the incisors of the voles are longer
+and the root of their last lower molar is lingual to the root of the
+incisor. Hinton thought also that the murine ancestors of microtines had
+shorter incisors and that the backward extension of the incisors in the
+voles is a more ancient feature than the hypsodonty of the molars. A
+trend in the molar teeth has been toward greater hypsodonty. The voles in
+which the molars are least hypsodont are thus considered primitive. These
+include the living genera _Clethrionomys_, _Phenacomys_, _Ondatra_,
+_Dolomys_, _Ellobius_, and _Prometheomys_. Therefore, the baculum, in
+these assumedly primitive genera, would be expected to resemble the
+baculum in the lemmings or at least the most primitive lemmings. This is
+not the case.
+
+The bacula that I have examined of _Clethrionomys_ and _Phenacomys_ have
+well-developed digital ossifications. In this they resemble the baculum
+of the genus _Lemmus_, the most advanced genus of lemmings according to
+Hinton. The baculum of _Dolomys_ has not been studied. The baculum in
+_Ondatra_, and in _Prometheomys_ as illustrated by Ognev (1948:552), also
+possesses well-developed processes. The baculum of _Ellobius_ is small
+and lacks processes (as figured by Ognev, 1950:662). No ossification was
+found in a single specimen of _Ellobius_ examined by me although the
+entire glans penis was removed and cleared without dissection. So far as
+known then, with the exception of _Ellobius_ and _Phenacomys longicaudus_
+(Dearden, 1958:547), the primitive microtines having rooted molars
+possess bacula having three well-developed ossified processes.
+
+Voles of the genus _Microtus_ vary in the structure of the baculum almost
+as much as do the lemmings. Within the single subgenus _Microtus_ some
+individuals of _Microtus mexicanus_, for example, have minute ossified
+lateral processes and other individuals lack these processes; _Microtus
+pennsylvanicus_ and some other species have proportionately large lateral
+ossifications. If the well-developed condition of the baculum in the
+microtines having rooted molars is primitive, then within the genus
+_Microtus_ those species having well-developed bacula may be considered
+primitive.
+
+The genera _Lagurus_ and _Neofiber_ have moderately developed or
+well-developed lateral processes. _Neofiber_ exhibits a tendency, not
+prominent elsewhere, to have a proportionately smaller median process
+rather than reduced lateral processes.
+
+American species of _Microtus_ (genus and subgenus) that have moderately-
+to well-developed ossified lateral processes are _M. townsendii_, _M.
+oeconomus_, _M. pennsylvanicus_, _M. montanus_, and _M. chrotorrhinus_.
+_Microtus_ of other subgenera having this type of baculum include _M.
+(Herpetomys) guatemalensis_, _M. (Chilotus) oregoni_, and _M. (Chionomys)
+longicaudus_.
+
+American species of _Microtus_ (genus and subgenus) in which the lateral
+ossifications are weakly developed or absent (although cartilaginous
+lateral processes are present) include _M. mexicanus_ and _M.
+californicus_. In other subgenera, species of _Microtus_ having reduced
+lateral ossifications are _M. (Pedomys) ochrogaster_, _M. (Pitymys)
+pinetorum_, _M. (Pitymys) parvulus_, _M. (Pitymys) quasiater_, _M.
+(Arvicola) richardsoni_, and _M. (Stenocranius) miurus_.
+
+The microtines are essentially holarctic in distribution. Both of the
+tribes, the lemmings and the voles, as well as primitive representatives
+of each tribe (not considering _Ellobius_) occur in both the Old World
+and New World. It is not certain on which continent (or continents) the
+Microtinae first differentiated. It is certain, however, that at various
+times, both early and late in the evolution of the subfamily,
+representatives have crossed from Eurasia to North America or _vice
+versa_. Each of 10 or more microtines in the New World is more closely
+related to some microtine in the Old World than to any other microtine in
+the New World.
+
+The similarities or differences in the baculum in Old World and New World
+representatives placed in the same genus or subgenus, or thought to be
+"companion species" have been commented upon in accounts of _Lemmus_,
+_Dicrostonyx_, _Clethrionomys_, _Lagurus_, _Arvicola_, _Stenocranius_,
+_Chilotus_, _Chionomys_, _Pitymys_, and in accounts of _Microtus
+agrestis_ as compared with _M. pennsylvanicus_, and _Microtus oeconomus_
+(both Old World and New World).
+
+The baculum in the Microtinae more closely resembles the baculum in the
+Cricetinae of the Old World than in the Murinae, or than in any other
+rodents known to me. This resemblance suggests relationship between
+Microtinae and Cricetinae.
+
+
+
+
+LITERATURE CITED
+
+
+ARGYROPULO, A. I.
+
+  1933a. Die Gattungen und Arten der Hamster (_Cricetinae_ Murray, 1866)
+  der Paläarktik. Zeitschr. f. Säugetierkunde, 8:129-149, 27 figs. in
+  text.
+
+  1933b. Über zwei neue paläarktische Wühlmäuse. Zeitschr. f.
+  Säugetierkunde, 8:180-183, 3 figs. in text.
+
+CALLERY, R.
+
+  1951. Development of the os genitale in the golden hamster,
+  _Mesocricetus (Cricetus) auratus_. Jour. Mamm., 32:204-207, 1 fig. in
+  text.
+
+CHAMBERLAIN, J. L.
+
+  1954. The Block Island meadow mouse, _Microtus provectus_. Jour. Mamm.,
+  35:587-589, 2 tables in text.
+
+DEARDEN, L. C.
+
+  1958. The baculum in _Lagurus_ and related microtines. Jour. Mamm.,
+  39:541-553, 1 fig. in text.
+
+DIDIER, R.
+
+  1943. L'os pénien des Campagnols de France du Genre _Arvicola_.
+  Mammalia, 7:74-79, 10 figs. in text.
+
+  1954. Etude systématique de l'os pénien des Mammifères (suite),
+  Rongeurs: Muridés. Mammalia, 18:237-256, 14 figs. in text.
+
+ELLERMAN, J. R.
+
+  1941. The families and genera of living rodents. Vol. II. Family
+  Muridae. The British Museum (Natural History), London, pp. xii + 690,
+  50 figs.
+
+FRILEY, CHARLES E.
+
+  1947. Preparation and preservation of the baculum of mammals. Jour.
+  Mamm., 28:395-397, 1 fig. in text.
+
+HALL, E. R., and E. L. COCKRUM.
+
+  1953. A synopsis of the North American microtine rodents. Univ. Kansas
+  Publ., Mus. Nat. Hist., 5:373-498, 149 figs. in text.
+
+HAMILTON, W. J., JR.
+
+  1946. A study of the baculum in some North American Microtinae. Jour.
+  Mamm., 27:378-387, 3 figs. in text.
+
+HIBBARD, C. W., and G. C. RINKER.
+
+  1942. A new bog-lemming (Synaptomys) from Meade County, Kansas. Univ.
+  Kansas Sci. Bull., 28:25-35, 3 figs. in text.
+
+  1943. A new meadow mouse (_Microtus ochrogaster taylori_) from Meade
+  County, Kansas. Univ. Kansas Sci. Bull., 29:255-268, 5 figs. in text.
+
+HINTON, M. A. C.
+
+  1926. Monograph of the voles and lemmings (Microtinae), living and
+  extinct, Vol. I. British Museum (Natural History), London, pp. xvi +
+  488, plus 15 plates, 110 figs. in text.
+
+MATTHEY, R.
+
+  1953. Les Chromosomes des Muridae. Revue Suisse de Zoologie,
+  60:225-283, avec les planches 1 à 4 groupant 84 photomicrographies, 98
+  figures et 5 schemas dans le texte.
+
+  1955. Nouveaux documents sur les chromosomes des Muridae. Problèmes de
+  cytologie comparée et de taxonomie chez les Microtinae. Revue Suisse de
+  Zoologie, 62:163-206, avec 114 figures.
+
+MILLER, G. S.
+
+  1896. Genera and subgenera of voles and lemmings. North American Fauna
+  No. 12, pp. 1-85, 40 figs. and 3 plates in text.
+
+OGNEV, S. I.
+
+  1948. The mammals of Russia (USSR) and adjacent countries (The mammals
+  of Eastern Europe and Northern Asia), Vol. 6. Publ. Acad. Sci. USSR,
+  pp. 1-587, 260 figs., 12 maps, and 11 color plates in text (in
+  Russian).
+
+  1950. The mammals of Russia (USSR) and adjacent countries (The mammals
+  of Eastern Europe and Northern Asia), Vol. 7. Publ. Acad. Sci. USSR,
+  pp. 1-736, 347 figs., 15 maps, and 10 color plates in text (in
+  Russian).
+
+RUTH, E. B.
+
+  1934. The os priapi: A study in bone development. Anat. Rec.,
+  60:231-249, 16 figs. in 3 plates.
+
+SMITH, D. A., and J. B. FOSTER.
+
+  1957. Notes on the small mammals of Churchill, Manitoba. Jour. Mamm.,
+  38:98-115, 3 figs. and 3 tables in text.
+
+WHEELER, B.
+
+  1956. Comparison of the Block Island "species" of _Microtus_ with _M.
+  pennsylvanicus_. Evolution, 10:176-186, 4 figs. and 2 tables in text.
+
+WHITE, J. A.
+
+  1951. A practical method for mounting the bacula of small mammals.
+  Jour. Mamm., 32:125.
+
+ZIMMERMAN, K.
+
+  1955. Die Gattung _Arvicola_ Lac. im System der Microtinae.
+  Säugetierkundliche Mitteilungen, 3:110-112, 2 figs. in text.
+
+  _Transmitted August 14, 1959._
+
+28-774
+
+
+
+
+  UNIVERSITY OF KANSAS PUBLICATIONS
+  MUSEUM OF NATURAL HISTORY
+
+
+Institutional libraries interested in publications exchange may obtain
+this series by addressing the Exchange Librarian, University of Kansas
+Library, Lawrence, Kansas. Copies for individuals, persons working in a
+particular field of study, may be obtained by addressing instead the
+Museum of Natural History, University of Kansas, Lawrence, Kansas. There
+is no provision for sale of this series by the University Library which
+meets institutional requests, or by the Museum of Natural History which
+meets the requests of individuals. However, when individuals request
+copies from the Museum, 25 cents should be included, for each separate
+number that is 100 pages or more in length, for the purpose of defraying
+the costs of wrapping and mailing.
+
+* An asterisk designates those numbers of which the Museum's supply (not
+the Library's supply) is exhausted. Numbers published to date, in this
+series, are as follows:
+
+  Vol. 1.  Nos. 1-26 and index. Pp. 1-638, 1946-1950.
+
+  *Vol. 2. (Complete) Mammals of Washington. By Walter W. Dalquest. Pp.
+           1-444, 140 figures in text. April 9, 1948.
+
+  Vol. 3.  *1. The avifauna of Micronesia, its origin, evolution, and
+           distribution. By Rollin H. Baker. Pp. 1-359, 16 figures in
+           text. June 12, 1951.
+
+           *2. A quantitative study of the nocturnal migration of birds.
+           By George H. Lowery, Jr. Pp. 361-472, 47 figures in text. June
+           29, 1951.
+
+           3. Phylogeny of the waxwings and allied birds. By M. Dale
+           Arvey. Pp. 473-530, 49 figures in text, 13 tables. October 10,
+           1951.
+
+           4. Birds from the state of Veracruz, Mexico. By George H.
+           Lowery, Jr., and Walter W. Dalquest. Pp. 531-649, 7 figures in
+           text, 2 tables. October 10, 1951.
+
+Index. Pp. 651-681.
+
+  *Vol. 4. (Complete) American weasels. By E. Raymond Hall. Pp. 1-466, 41
+           plates, 31 figures in text. December 27, 1951.
+
+  Vol. 5.  Nos. 1-37 and index. Pp. 1-676, 1951-1953.
+
+  *Vol. 6. (Complete) Mammals of Utah, _taxonomy_ and _distribution_. By
+           Stephen D. Durrant. Pp. 1-549, 91 figures in text, 30 tables.
+           August 10, 1952.
+
+  Vol. 7.  *1. Mammals of Kansas. By E. Lendell Cockrum. Pp. 1-303, 73
+           figures in text, 37 tables. August 25, 1952.
+
+           2. Ecology of the opossum on a natural area in northeastern
+           Kansas. By Henry S. Fitch and Lewis L. Sandidge. Pp. 305-338,
+           5 figures in text. August 24, 1953.
+
+           3. The silky pocket mice (Perognathus flavus) of Mexico. By
+           Rollin H. Baker. Pp. 339-347, 1 figure in text. February 15,
+           1954.
+
+           4. North American jumping mice (Genus Zapus). By Phillip H.
+           Krutzsch. Pp. 349-472, 47 figures in text, 4 tables. April 21,
+           1954.
+
+           5. Mammals from Southeastern Alaska. By Rollin H. Baker and
+           James S. Findley. Pp. 473-477. April 21, 1954.
+
+           6. Distribution of Some Nebraskan Mammals. By J. Knox Jones,
+           Jr. Pp. 479-487. April 21, 1954.
+
+           7. Subspeciation in the montane meadow mouse, Microtus
+           montanus, in Wyoming and Colorado. By Sydney Anderson. Pp.
+           489-506, 2 figures in text. July 23, 1954.
+
+           8. A new subspecies of bat (Myotis velifer) from southeastern
+           California and Arizona. By Terry A. Vaughan. Pp. 507-512. July
+           23, 1954.
+
+           9. Mammals of the San Gabriel mountains of California. By
+           Terry A. Vaughan. Pp. 513-582, 1 figure in text, 12 tables.
+           November 15, 1954.
+
+           10. A new bat (Genus Pipistrellus) from northeastern Mexico.
+           By Rollin H. Baker. Pp. 583-586. November 15, 1954.
+
+           11. A new subspecies of pocket mouse from Kansas. By E.
+           Raymond Hall. Pp. 587-590. November 15, 1954.
+
+           12. Geographic variation in the pocket gopher, Cratogeomys
+           castanops, in Coahuila, Mexico. By Robert J. Russell and
+           Rollin H. Baker. Pp. 591-608. March 15, 1955.
+
+           13. A new cottontail (Sylvilagus floridanus) from
+           northeastern Mexico. By Rollin H. Baker. Pp. 609-612. April 8,
+           1955.
+
+           14. Taxonomy and distribution of some American shrews. By
+           James S. Findley. Pp. 613-618. June 10, 1955.
+
+           15. The pigmy woodrat, Neotoma goldmani, its distribution and
+           systematic position. By Dennis G. Rainey and Rollin H. Baker.
+           Pp. 619-624, 2 figures in text. June 10, 1955.
+
+Index. Pp. 625-651.
+
+  Vol. 8.  1. Life history and ecology of the five-lined skink, Eumeces
+           fasciatus. By Henry S. Fitch. Pp. 1-156, 26 figures in text.
+           September 1, 1954.
+
+           2. Myology and serology of the Avian Family Fringillidae, a
+           taxonomic study. By William B. Stallcup. Pp. 157-211, 23
+           figures in text, 4 tables. November 15, 1954.
+
+           3. An ecological study of the collared lizard (Crotaphytus
+           collaris). By Henry S. Fitch. Pp. 213-274, 10 figures in text.
+           February 10, 1956.
+
+           4. A field study of the Kansas ant-eating frog, Gastrophryne
+           olivacea. By Henry S. Fitch. Pp. 275-306, 9 figures in text.
+           February 10, 1956.
+
+           5. Check-list of the birds of Kansas. By Harrison B. Tordoff.
+           Pp. 307-359, 1 figure in text. March 10, 1956.
+
+           6. A population study of the prairie vole (Microtus
+           ochrogaster) in northeastern Kansas. By Edwin P. Martin. Pp.
+           361-416, 19 figures in text. April 2, 1956.
+
+           7. Temperature responses in free-living amphibians and
+           reptiles of northeastern Kansas. By Henry S. Fitch. Pp.
+           417-476, 10 figures in text, 6 tables. June 1, 1956.
+
+           8. Food of the crow, Corvus brachyrhynchos Brehm, in
+           south-central Kansas. By Dwight Platt. Pp. 477-498, 4 tables.
+           June 8, 1956.
+
+           9. Ecological observations on the woodrat Neotoma floridana.
+           By Henry S. Fitch and Dennis G. Rainey. Pp. 499-533, 3 figures
+           in text. June 12, 1956.
+
+           10. Eastern woodrat, Neotoma floridana; Life history and
+           ecology. By Dennis G. Rainey. Pp. 535-646, 12 plates, 13
+           figures in text. August 15, 1956.
+
+Index. Pp. 647-675.
+
+  Vol. 9.  1. Speciation of the wandering shrew. By James S. Findley. Pp.
+           1-68, 18 figures in text. December 10, 1955.
+
+           2. Additional records and extension of ranges of mammals from
+           Utah. By Stephen D. Durrant, M. Raymond Lee, and Richard M.
+           Hansen. Pp. 69-80. December 10, 1955.
+
+           3. A new long-eared myotis (Myotis evotis) from northeastern
+           Mexico. By Rollin H. Baker and Howard J. Stains. Pp. 81-84.
+           December 10, 1955.
+
+           4. Subspeciation in the meadow mouse, Microtus
+           pennsylvanicus, in Wyoming. By Sydney Anderson. Pp. 85-104, 2
+           figures in text. May 10, 1956.
+
+           5. The condylarth genus Ellipsodon. By Robert W. Wilson. Pp.
+           105-116, 6 figures in text. May 19, 1956.
+
+           6. Additional remains of the multituberculate genus
+           Eucosmodon. By Robert W. Wilson. Pp. 117-123, 10 figures in
+           text. May 19, 1956.
+
+           7. Mammals of Coahuila, Mexico. By Rollin H. Baker. Pp.
+           125-335, 75 figures in text. June 15, 1956.
+
+           8. Comments on the taxonomic status of Apodemus peninsulae,
+           with description of a new subspecies from North China. By J.
+           Knox Jones, Jr. Pp. 337-346, 1 figure in text, 1 table. August
+           15, 1956.
+
+           9. Extensions of known ranges of Mexican bats. By Sydney
+           Anderson. Pp. 347-351. August 15, 1956.
+
+           10. A new bat (Genus Leptonycteris) from Coahuila. By Howard
+           J. Stains. Pp. 353-356. January 21, 1957.
+
+           11. A new species of pocket gopher (Genus Pappogeomys) from
+           Jalisco, Mexico. By Robert J. Russell. Pp. 357-361. January
+           21, 1957.
+
+           12. Geographic variation in the pocket gopher, Thomomys
+           bottae, in Colorado. By Phillip M. Youngman. Pp. 363-387, 7
+           figures in text. February 21, 1958.
+
+           13. New bog lemming (genus Synaptomys) from Nebraska. By J.
+           Knox Jones, Jr. Pp. 385-388. May 12, 1958.
+
+           14. Pleistocene bats from San Josecito Cave, Nuevo León,
+           México. By J. Knox Jones, Jr. Pp. 389-396. December 19, 1958.
+
+           15. New subspecies of the rodent Baiomys from Central
+           America. By Robert L. Packard. Pp. 397-404. December 19, 1958.
+
+           16. Mammals of the Grand Mesa, Colorado. By Sydney Anderson.
+           Pp. 405-414, 1 figure in text, May 20, 1959.
+
+           17. Distribution, variation, and relationships of the montane
+           vole, Microtus montanus. By Sydney Anderson. Pp. 415-511, 12
+           figures in text, 2 tables. August 1, 1959.
+
+           18. Conspecificity of two pocket mice, Perognathus goldmani
+           and P. artus. By E. Raymond Hall and Marilyn Bailey Ogilvie.
+           Pp. 513-518, 1 map in text. January 14, 1960.
+
+           19. Records of harvest mice, Reithrodontomys, from Central
+           America, with description of a new subspecies from Nicaragua.
+           By Sydney Anderson and J. Knox Jones, Jr. Pp. 519-529. January
+           14, 1960.
+
+           20. Small carnivores from San Josecito Cave (Pleistocene),
+           Nuevo León, México. By E. Raymond Hall. Pp. 531-538, 1 figure
+           in text. January 14, 1960.
+
+           21. Pleistocene pocket gophers from San Josecito Cave, Nuevo
+           León, México. By Robert J. Russell. Pp. 539-548, 1 figure in
+           text, January 14, 1960. More numbers will appear in volume 9.
+
+  Vol. 10. 1. Studies of birds killed in nocturnal migration. By Harrison
+           B. Tordoff and Robert M. Mengel. Pp. 1-44, 6 figures in text,
+           2 tables. September 12, 1956.
+
+           2. Comparative breeding behavior of Ammospiza caudacuta and
+           A. maritima. By Glen E. Woolfenden. Pp. 45-75, 6 plates, 1
+           figure. December 20, 1956.
+
+           3. The forest habitat of the University of Kansas Natural
+           History Reservation. By Henry S. Fitch and Ronald R. McGregor.
+           Pp. 77-127, 2 plates, 7 figures in text, 4 tables. December
+           31, 1956.
+
+           4. Aspects of reproduction and development in the prairie
+           vole (Microtus ochrogaster). By Henry S. Fitch. Pp. 129-161, 8
+           figures in text, 4 tables. December 19, 1957.
+
+           5. Birds found on the Arctic slope of northern Alaska. By
+           James W. Bee. Pp. 163-211, plates 9-10, 1 figure in text.
+           March 12, 1958.
+
+           6. The wood rats of Colorado: distribution and ecology. By
+           Robert B. Finley, Jr. Pp. 213-552, 34 plates, 8 figures in
+           text, 35 tables. November 7, 1958.
+
+           7. Home ranges and movements of the eastern cottontail in
+           Kansas. By Donald W. Janes. Pp. 553-572, 4 plates, 3 figures
+           in text. May 4, 1959.
+
+           8. Natural history of the salamander Aneides hardyi. By
+           Richard F. Johnston and Gerhard A. Schad. Pp. 573-585. October
+           8, 1959.
+
+More numbers will appear in volume 10.
+
+  Vol. 11. 1. The systematic status of the colubrid snake, Leptodeira
+           discolor Günther. By William E. Duellman. Pp. 1-9, 4 figures.
+           July 14, 1958.
+
+           2. Natural history of the six-lined racerunner, Cnemidophorus
+           sexlineatus. By Henry S. Fitch. Pp. 11-62, 9 figures, 9
+           tables. September 19, 1958.
+
+           3. Home ranges, territories, and seasonal movements of
+           vertebrates of the Natural History Reservation. By Henry S.
+           Fitch. Pp. 63-326, 6 plates, 24 figures in text, 3 tables.
+           December 12, 1958.
+
+           4. A new snake of the genus Geophis from Chihuahua, Mexico.
+           By John M. Legler. Pp. 327-334, 2 figures in text. January 28,
+           1959.
+
+           5. A new tortoise, genus Gopherus, from north-central Mexico.
+           By John M. Legler. Pp. 335-343. April 24, 1959.
+
+           6. Fishes of Chautauqua, Cowley and Elk counties, Kansas. By
+           Artie L. Metcalf. Pp. 345-400, 2 plates, 2 figures in text, 10
+           tables. May 6, 1959.
+
+           7. Fishes of the Big Blue River Basin, Kansas. By W. L.
+           Minckley. Pp. 401-442, 2 plates, 4 figures in text, 5 tables.
+           May 8, 1959.
+
+           8. Birds from Coahuila, México. By Emil K. Urban. Pp.
+           443-516. August 1, 1959.
+
+           9. Description of a new softshell turtle from the
+           southeastern United States. By Robert G. Webb. Pp. 517-525, 2
+           plates, 1 figure in text. August 14, 1959.
+
+Another number will appear in volume 11.
+
+  Vol. 12. 1. Functional morphology of three bats: Eumops, Myotis,
+           Macrotus. By Terry A. Vaughan. Pp. 1-153, 4 plates, 24 figures
+           in text. July 8, 1959.
+
+           2. The ancestry of modern Amphibia: a review of the evidence.
+           By Theodore H. Eaton, Jr. Pp. 155-180, 10 figures in text.
+           July 10, 1959.
+
+           3. The baculum in microtine rodents. By Sydney Anderson. Pp.
+           181-216, 49 figures in text. February 19, 1960.
+
+More numbers will appear in volume 12.
+
+
+
+
+
+
+End of the Project Gutenberg EBook of The Baculum in Microtine Rodents, by 
+Sydney Anderson
+
+*** END OF THIS PROJECT GUTENBERG EBOOK THE BACULUM IN MICROTINE RODENTS ***
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+Title: The Baculum in Microtine Rodents
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+Author: Sydney Anderson
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+
+
+<p class="smcap center">University of Kansas Publications<br />
+Museum of Natural History</p>
+
+<p class="center">Volume 12, No. 3, pp. 181-216, 49 figs.<br />
+February 19, 1960</p>
+
+<h1>The Baculum in Microtine Rodents</h1>
+
+<p class="center" style="font-size:larger;">BY<br />
+SYDNEY ANDERSON</p>
+
+<p class="smcap center" style="margin-top:3em;">University of Kansas<br />
+Lawrence<br />
+1960</p>
+
+<p class="smcap center" style="margin-top:3em;">University of Kansas Publications, Museum of Natural History</p>
+
+<p class="center">Editors: E. Raymond Hall, Chairman, Henry S. Fitch, Robert W. Wilson</p>
+
+<p class="center">Volume 12, No. 3, pp. 181-216, 49 figs.<br />
+Published February 19, 1960</p>
+
+<p class="center"><span class="smcap">University of Kansas</span><br />
+Lawrence, Kansas</p>
+
+<p class="center" style="font-size:smaller;">PRINTED IN<br />
+THE STATE PRINTING PLANT<br />
+TOPEKA, KANSAS<br />
+1960</p>
+
+<div class="imgcenter" style="width: 100px;">
+<img src="images/001.jpg" width="100" height="39" alt="" title="" />
+</div>
+
+<p class="center">28-774</p>
+
+
+<hr />
+
+<p><span class="pagenum"><a name="Page_183" id="Page_183">[Pg 183]</a></span></p>
+
+<p class="center" style="font-size:2em;">The Baculum in Microtine Rodents</p>
+<p class="center">BY<br />SYDNEY ANDERSON</p>
+
+<h2>INTRODUCTION</h2>
+
+<p>Didier (1943, 1954) has described the bacula of several Old World
+microtines, and other rodents. Argyropulo studied (1933a, 1933b) five
+species of Cricetinae and <i>Microtus socialis</i>. Ognev (1950)
+illustrated numerous species of Eurasian microtines. Hamilton (1946)
+figured and described the baculum of 11 species of North American
+microtines. Hibbard and Rinker (1942, 1943) figured the baculum of
+<i>Synaptomys cooperi paludis</i> and of <i>Microtus ochrogaster
+taylori</i>. Dearden (1958) studied the baculum in two Asiatic species of
+<i>Lagurus</i>, in six subspecies of <i>Lagurus curtatus</i> of North
+America, and in six other species of microtines of other genera.</p>
+
+<p>The baculum can be preserved easily with standard study skins, and is
+potentially useful in interpreting relationships on any taxonomic level,
+and especially in determining the relationships of species within a
+genus, if used together with other structures.</p>
+
+<p>The anatomical orientation of the baculum needs comment because some
+confusion exists in the literature, especially concerning the use of the
+terms ventral and dorsal. The urethra lies on the anatomically ventral
+side of the penis, and of the baculum. In the center of the penis lies a
+single corpus cavernosum penis, shown in cross section proximal to the
+baculum in Figure 1c. Dorsally an artery, thinner walled than the ventral
+urethra, ends in a somewhat reticulate sinus surrounding primarily the
+middle part of the baculum within the bulbous glans penis. The corpus
+cavernosum penis (the structure has no median septum, at least distally)
+terminates with the baculum and is closely knit to it. The site of this
+bond is evident in the tuberosities and sculpturing of the base of the
+baculum.</p>
+
+<p>The part of the penis enclosing the baculum, when not erect, is folded
+back as shown in Figures 1a and 1b. As a result the anatomically ventral
+surface faces upwards, or at least posterodorsally. The use of the term
+ventral in this account refers to the anatomically ventral side, that is
+to say to the side of the baculum facing the urethra.</p>
+
+<p>The baculum in microtines consists of an elongate stalk, having a
+laterally, and to a lesser extent dorsoventrally, expanded base and
+
+<span class="pagenum"><a name="Page_184" id="Page_184">[Pg
+184]</a></span>
+
+an attenuate distal shaft. Usually, three digitate processes of
+cartilaginous material in which additional ossifications may occur arise
+from the terminus of the shaft. The proportions and curvature of the
+stalk vary as do the proportions of the terminal ossifications to each
+other and to the stalk. In some species one or more of the digital
+processes are frequently completely unossified.</p>
+
+<div class="imgcenter" style="width: 500px;">
+<img src="images/184a.jpg" width="500" height="203" alt="Diagram a, b, c." title="" />
+</div>
+
+<div class="imgcenter" style="width: 500px;">
+<img src="images/184b.jpg" width="500" height="268" alt="Graph. X-axis: Length of Animal in Millimeters. Y-axis: Length of Stalk of Baculum in Millimeters." title="" />
+</div>
+
+<p><span class="smcap">Figure 1.</span> The
+baculum in <i>Microtus ochrogaster</i>&mdash;orientation and variation
+with age. <i>a.</i> Diagram of a sagittal section of the posterior half
+of a vole, natural size. The penis, containing the baculum (in black),
+extends ventrally from a point posterior to the pubic symphysis
+(stippled), along the body wall, and bends posteriorly at the distal end.
+<i>b.</i> Distal end of penis (&times; 2) showing baculum (in black), the
+urethra (solid lines) adjacent to the baculum, and the corpus cavernosum
+(broken lines) proximal to the baculum. <i>c.</i> Oblique view of the
+cross section of penis (&times; 4) shown in Figure 1 <i>b</i>. The
+thick-walled urethra lies ventral to the curved corpus cavernosum. A
+thinner-walled blood-vessel lies dorsal to the corpus cavernosum. The
+anatomically ventral side of the baculum, in the normal non-erect penis
+shown, is seen to face dorsally. <i>d.</i> Graph showing the relationship
+between size of baculum, size of animal, and development of digital
+ossifications. Circles show presence of ossification in stalk only;
+circles enclosing dots indicate presence of secondary ossification in
+median process also; large dots indicate the addition of tertiary
+ossification in one or both of the lateral digitate processes.</p>
+
+<p><span class="pagenum"><a name="Page_185" id="Page_185">[Pg
+185]</a></span></p>
+
+<p>Preserved specimens of <i>Microtus arvalis</i>, <i>Microtus
+agrestis</i>, <i>Microtus orcadensis</i>, <i>Microtus nivalis</i>,
+<i>Microtus guentheri</i>, <i>Microtus subterraneus</i>, <i>Clethrionomys
+glareolus</i>, and <i>Ellobius lutescens</i> were provided by Prof.
+Robert Matthey of Lausanne, Switzerland. J. Knox Jones, Jr. carefully
+saved the bacula with specimens of <i>Microtus fortis</i> and
+<i>Clethrionomys rufocanus</i> from Korea. Dr. W. B. Quay, Department of
+Zoology, University of California, supplied specimens of <i>Synaptomys
+cooperi</i>, <i>Phenacomys intermedius</i>, and <i>Microtus oregoni</i>.
+Dr. Franklin Sturges and Mr. John W. Goertz, Museum of Natural History,
+Oregon State College, Corvallis, have provided specimens including bacula
+of <i>Clethrionomys occidentalis</i>, <i>Microtus oregoni</i>, and
+<i>Microtus townsendii</i>. Dr. Randolph L. Peterson and Mr. Bristol
+Foster, Royal Ontario Museum of Zoology, Toronto, Canada, provided
+specimens of <i>Phenacomys intermedius</i>. Dr. J. N. Layne, University
+of Florida, Gainsville, Florida, presented me with a baculum of
+<i>Microtus parvulus</i>.</p>
+
+<p>I am indebted to all of these persons for their aid, and to various
+collectors for the Museum of Natural History, who preserved bacula with
+specimens. Many of these specimens were obtained through the assistance
+of the University of Kansas Endowment Association and the National
+Science Foundation.</p>
+
+
+<h2>METHODS</h2>
+
+<p>Bacula were obtained from fresh specimens, specimens preserved in
+alcohol or formalin, and dried study skins. The processing of bacula has
+been discussed by Hamilton (1946), Friley (1947), White (1951), and
+Dearden (1958). The methods used to preserve bacula for my study differed
+some from any of those reported. The terminal part of each penis
+including the baculum imbedded in the glans penis was removed in its
+entirety and placed in a vial. The catalogue number was kept with each
+specimen at all times. A two per cent solution of potassium hydroxide was
+added. All specimens were examined at least once a day. If tissues other
+than the glans penis were present they were removed with forceps when
+softened usually at the end of one day. Several drops of Alizarin red-S
+stain in a saturated alcoholic solution were added to the 3 to 5 ccs. of
+KOH solution in each vial. Solutions were replaced if they became turbid
+enough to obstruct observation of the clearing penis. After one day the
+solution containing stain was removed and replaced with two per cent KOH
+solution without stain. When the glans became sufficiently cleared that
+the stained baculum could be seen easily, the solution was replaced by
+glycerin in which clearing was completed. The time required for the
+entire process varied from one day to more than two weeks depending on
+the size of the specimen and on its condition. Fresh specimens clear more
+rapidly than dried specimens, and those that are dried more rapidly than
+those that are preserved. A three or four per cent solution of hydroxide
+will hasten the process, but more frequent observation is required to
+prevent excessive maceration.</p>
+
+<p>Specimens were then examined in a shallow dish containing glycerin
+under a binocular microscope. The baculum can be viewed from any desired
+direction. The method described above leaves the baculum intact within
+the glans penis; therefore its orientation can be determined relative to
+the thick walled urethra and the thin walled dorsal artery that extends
+onto the dorsal side of the baculum. The ventral curvature of the penis
+proximal to the baculum, and the distal extension, characteristic of most
+species, of the dorsal border of
+
+<span class="pagenum"><a name="Page_186" id="Page_186">[Pg
+186]</a></span>
+
+the glans (both shown in Figure 1) are other features aiding in correctly
+orienting cleared specimens. The digitate processes are not so often
+injured, lost, or displaced when the method described above is used as
+they are when the penis is dissected. Specimens were stored in glycerin
+in glass shell vials having polyethylene stoppers. A small card bearing
+the name, number, locality, and other data was placed in each vial. A
+specimen thus enclosed can be kept indefinitely, or removed and mounted
+in balsam as described by White (1951:631) or in plastic as described by
+Dearden (1958:541) and thus stored in the vial containing the skull of
+the specimen.</p>
+
+<p>Drawings were made on millimeter ruled paper while the baculum was
+viewed under a binocular microscope with a square ruled eyepiece.</p>
+
+<p>Unless otherwise noted all specimens listed are in the University of
+Kansas Museum of Natural History. Catalogue numbers are cited.
+Measurements are accurate to within less than one-tenth of a millimeter.
+Proportions as stated in the text are approximations, accurate to within
+one-twelfth (8.33 per cent). The range of variation is unknown for some
+species. Mention is made if maturity is known or suspected to differ in
+specimens being compared.</p>
+
+<p>The development of the baculum has been studied by Callery (1951) in
+<i>Mesocricetus auratus</i> and by Ruth (1934) in the laboratory rat. In
+the rat (<i>Rattus norvegicus</i>) the bone is of endoblastemal origin
+being laid down by a condensation of undifferentiated mesenchymal cells.
+At the distal end of the bone dense fibrous tissue is then differentiated
+and at the proximal end hyaline cartilage. Growth is by substitution at
+the proximal end and by subperiosteal lamellation circumferentially. A
+marrow cavity is formed by resorption. In the baculum of the hamster the
+primary center of ossification is in the stalk, and is present at the age
+of three days; the secondary centers are in lateral processes and are
+present at 80 days and enlarge subsequently. A tertiary center, in each
+median process, may or may not develop later. Maximum development of the
+baculum is reached late in the reproductive life of the hamster.</p>
+
+<p>The early ossification of the baculum noted in the rat and the hamster
+occurs in <i>Microtus</i> also. A specimen of <i>Microtus montanus
+fusus</i> (76831, from 5 mi. N, 26 mi. W Saguache, 9600 ft., Saguache
+County, Colorado) only 74 mm. in total length and weighing only 6.6
+grams, had a slender ossified baculum having enlarged ends. This vole was
+one-half of the average length and less than one-fifth of the average
+weight of an adult, and of approximately the size at which weaning takes
+place.</p>
+
+<p>The development of the baculum in <i>Microtus ochrogaster</i> was
+studied in 32 specimens of various ages. The specimens (between Nos.
+74994 and 75074) were collected between August 15 and September 4, 1957,
+at localities on the Great Plains. These specimens were from breeding
+populations, as evidenced by pregnancy of females and by large size of
+testes of males. The length and width of the stalk of the baculum, the
+presence of digital ossifications, the
+
+<span class="pagenum"><a name="Page_187" id="Page_187">[Pg
+187]</a></span>
+
+total length of the animal, and the size of the testes were noted.
+Variability in length of testes is greatest when voles are from 140 to
+150 mm. in total length. Sexual maturity is reached rather abruptly when
+the total length of most individuals is 140 to 150 millimeters. If the
+baculum likewise underwent more rapid growth at the onset of sexual
+maturity, greater variability should be evident in the length of the
+baculum of voles 140 to 150 mm. in total length than in bacula of voles
+of other sizes. This was the case (see Figure 1d). The baculum does not,
+however, suddenly reach its maximum maturity.</p>
+
+<p>The primary ossification is in the stalk. The secondary ossification
+is in the median process except in <i>Lagurus</i> (Dearden, 1958:551) and
+some individuals of <i>Neofiber</i> (see account on page 258). Tertiary
+centers of ossification are in the lateral processes. The primary
+ossification is present at an early age and subsequently increases in
+size and solidity. The secondary and tertiary ossifications are
+progressively more common in older voles. The increase in degree of
+ossification of all parts continues after sexual maturity is reached.
+Individual variation and variation with age in the baculum of <i>Microtus
+pennsylvanicus</i> have been illustrated by Hamilton (1946:380). Figures
+14, 15, and 17 illustrate variation with size, which is correlated with
+age, and also illustrate individual variation. The three bacula are from
+adult voles having testes that measured 15, 16 and 16 mm. in length,
+respectively. Each vole was trapped in late June. The total lengths in
+millimeters of the three voles are 172, 167, and 181; weights are 55,
+52.4, and 65.5 grams. I judge that the greater size of the stalk and the
+better developed base shown in Figure 17 than in Figure 15 are
+illustrative of age variation; the difference in the size of the lateral
+digitate processes is, in this case, attributable to individual
+variation. Differences in the distal end of the baculum in Figures 42 and
+43, show individual variation also. Figures 35 and 36 represent two
+different subspecies; different individuals of <i>M. mexicanus
+mogollonensis</i>, however, exhibit individual variation of the same
+degree.</p>
+
+<p>Hall and Cockrum (1953) list 44 species of microtines in North
+America. At least twelve of these are insular or local forms perhaps
+derived from some other species; for example <i>Microtus coronarius</i>,
+an insular form derived from <i>Microtus longicaudus</i>; <i>Microtus
+provectus</i>, considered by Chamberlain (1954:587) and by Wheeler
+(1956:176) as a subspecies of <i>Microtus pennsylvanicus</i>; and
+<i>Microtus ludovicianus</i>, a close relative of <i>Microtus
+ochrogaster</i>.</p>
+
+<p>All North American genera have been studied. Of the genus
+<i>Microtus</i> in North America, all subgenera but <i>Orthriomys</i> and
+all species but the following nine, have been studied: <i>M. (Orthriomys)
+umbrosus</i>, the insular <i>M. (Stenocranius) abbreviatus</i>, <i>M.
+(Microtus) breweri</i>, <i>M. (Microtus) nesophilus</i>, <i>M.</i></p>
+
+<p><span class="pagenum"><a name="Page_188" id="Page_188">[Pg
+188]</a></span></p>
+
+<div class="imgcenter" style="width: 421px;">
+<img src="images/188.jpg" width="421" height="500" alt="" title="" />
+</div>
+
+<p><span class="smcap">Figures</span> 2-13. Bacula of microtines. Unless
+indicated otherwise views are (<i>a</i>) of the dorsum, (<i>b</i>) the
+right side, and (<i>c</i>) the proximal end with the dorsal surface
+upward. Exact localities are given in accounts of species concerned.</p>
+
+<ol id="start_02">
+	<li><i>Lemmus trimucronatus</i>, 50678, Point Barrow, Alaska.</li>
+	<li><i>Dicrostonyx groenlandicus</i>, 50539, Porcupine Lake, Brooks Range,
+	Alaska.</li>
+	<li><i>Dicrostonyx groenlandicus</i>, 52524, Point Barrow, Alaska.</li>
+	<li><i>Synaptomys cooperi saturatus</i>, WBQ 3-C-454, 3 mi. S Demotte, Indiana.</li>
+	<li><i>Synaptomys cooperi paludis</i>, 13716, Meade County State Park, Kansas.</li>
+	<li><i>Phenacomys intermedius celatus</i>, SA 2044, Quebec.</li>
+	<li><i>Phenacomys intermedius intermedius</i>, WBQ 3-C-309, 5.4 mi. S Moran,
+	Teton Co., Wyoming.</li>
+	<li><i>Clethrionomys rufocanus</i>, 60438, 1 mi. NW Oho-ri, Korea, (<i>d</i>) ventral
+	view.</li>
+	<li><i>Clethrionomys gapperi</i>, 42108, 31 mi. N Pinedale, Wyoming.</li>
+	<li><i>Clethrionomys rutilus</i>, 42865, 5 mi. NNE Gulkana, Alaska.</li>
+	<li><i>Clethrionomys occidentalis</i>, FWS 30, Mary's Peak, Benton Co., Oregon.</li>
+	<li><i>Clethrionomys glareolus</i>, 67100, Zermatt, Valais, Switzerland.</li>
+</ol>
+
+<p><span class="pagenum"><a name="Page_189" id="Page_189">[Pg
+189]</a></span></p>
+
+<div class="imgcenter" style="width: 431px;">
+<img src="images/189.jpg" width="431" height="500" alt="" title="" />
+</div>
+
+<p><span class="smcap">Figures</span> 14-25. Bacula of <i>Microtus</i>.
+Unless indicated otherwise views are (<i>a</i>) of the dorsum, (<i>b</i>)
+the right side, and (<i>c</i>) the proximal end with dorsal surface
+upward.</p>
+
+<ol id="start_14">
+	<li><i>M. pennsylvanicus</i>, 42439, 1 mi. S, 2 mi. E Eagle Nest, Colfax
+Co., New Mexico; abnormality perhaps owing to injury; dorsal view.</li>
+	<li><i>M. pennsylvanicus</i>, 42306, 5 mi. N, 26 mi. W Saguache, Colorado;
+	dorsal view.</li>
+	<li><i>M. pennsylvanicus</i>, 43043, 20 mi. NE Anchorage, Alaska, ventral view.</li>
+	<li><i>M. pennsylvanicus</i>, 42430, 1 mi. S, 2 mi. E Eagle Nest, New Mexico.</li>
+	<li><i>M. agrestis</i>, 67102, Gryon, Switzerland.</li>
+	<li><i>M. montanus amosus</i>, 62241, 1/2 mi. E Soldier Summit, Wasatch Co.,
+	Utah.</li>
+	<li><i>M. montanus nanus</i>, 57470, 2 mi. N, 2 mi. W Pocatello, Idaho.</li>
+	<li><i>M. montanus fusus</i>, 42307, 5 mi. N, 26 mi. W Saguache, Colorado.</li>
+	<li><i>M. arvalis</i>, 67101, Vidy, Switzerland, possibly not mature.</li>
+	<li><i>M. guentheri</i>, 67104, Palestine.</li>
+	<li><i>M. orcadensis</i>, 67106, Orkney Islands, orientation uncertain.</li>
+	<li><i>M. fortis</i>, 63841, Chipo-ri, Korea, (<i>d</i>) ventral view.</li>
+</ol>
+
+<p><span class="pagenum"><a name="Page_190" id="Page_190">[Pg
+190]</a></span></p>
+
+<div class="imgcenter" style="width: 432px;">
+<img src="images/190.jpg" width="432" height="500" alt="" title="" />
+</div>
+
+<p><span class="smcap">Figures</span> 26-39. Bacula of microtines. Unless indicated
+otherwise views are (<i>a</i>) of the dorsum, (<i>b</i>) the right side,
+and (<i>c</i>) the proximal end with the dorsal surface upward.</p>
+
+<ol id="start_25">
+	<li><i>M. (Pitymys) fatioi</i>, 67103, Zermatt, Switzerland, immature.</li>
+	<li><i>M. (Pitymys) pinetorum</i>, 76834, 2 mi. N Baldwin, Douglas Co., Kansas.</li>
+	<li><i>M. (Pitymys) pinetorum</i>, 68545, 1 mi. NE Pleasant Grove, Kansas.</li>
+	<li><i>M. (Pitymys) quasiator</i>, 30709, Teocelo, Veracruz, (<i>d</i>) ventral view.</li>
+	<li><i>M. (Pitymys) quasiator</i>, 19878, 5 km. N Jalapa, Veracruz.</li>
+	<li><i>M. (Pedomys) ochrogaster</i>, 75036, 1 mi. N, 2 mi. E Oberlin, Kansas.</li>
+	<li><i>M. (Stenocranius) miurus</i>, 51152, Lake Schrader, Brooks Range, Alaska.</li>
+	<li><i>M. (Stenocranius) miurus</i>, 51169, Lake Schrader, Brooks Range, Alaska.</li>
+	<li><i>M. (Stenocranius) gregalis</i>, 8059, "Eastern Europe."</li>
+	<li><i>M. mexicanus mexicanus</i>, 63094, Valle de Bravo, Estado de M&eacute;xico, M&eacute;xico.</li>
+	<li><i>M. mexicanus mogollonensis</i>, 63298, Mt. Taylor, Valencia Co., New Mexico.</li>
+	<li><i>M. californicus</i>, 76828, 1 mi. NE Berkeley, California; (<i>d</i>) ventral view.</li>
+	<li><i>M. (Arvicola) richardsoni</i>, 42454, 31 mi. N Pinedale, Sublette Co., Wyoming.</li>
+	<li><i>M. richardsoni</i>, 37903, 23-1/2 mi. S, 5 mi. W Lander, Wyoming; distal end.</li>
+</ol>
+
+<p><span class="pagenum"><a name="Page_191" id="Page_191">[Pg
+191]</a></span></p>
+
+<div class="imgcenter" style="width: 420px;">
+<img src="images/191.jpg" width="420" height="500" alt="" title="" />
+</div>
+
+<p><span class="smcap">Figures</span> 40-49. Bacula of microtines. Unless
+indicated otherwise views are (<i>a</i>) of the dorsum, (<i>b</i>) the
+right side, and (<i>c</i>) the proximal end with the dorsal surface
+upward.</p>
+
+<ol id="start_39">
+	<li><i>Microtus (Pitymys) parvulus</i>, UF 1508, 1 mi. W Micanopy, Florida.</li>
+	<li><i>Microtus townsendii</i>, 79186, Sec. 33, T. 11S, R. 5W, Benton Co., Oregon.</li>
+	<li><i>Microtus (Herpetomys) guatemalensis</i>, 65895, 2 mi. S San Juan Ixcoy, Guatemala.</li>
+	<li><i>M. guatemalensis</i>, 65921, 10 mi. E, 4 mi. S Totonicapan, Guatemala, dorsal view
+	of tip.</li>
+	<li><i>Microtus oeconomus</i>, 43048, Kelsall Lake, British Columbia.</li>
+	<li><i>Microtus (Chilotus) oregoni</i>, WBQ 3-C-248, 5 mi. N Orick, California.</li>
+	<li><i>Lagurus (Lemmiscus) curtatus</i>, 26053, 9 mi. S Robertson, Uinta Co., Wyoming.</li>
+	<li><i>Microtus (Chionomys) nivalis</i>, 65127, Wetterstein, Germany, orientation uncertain.</li>
+	<li><i>Microtus (Chionomys) longicaudus</i>, 50253, Crane Flat, Mariposa Co., California.</li>
+	<li><i>Neofiber alleni</i>, 27268, 2 mi. S Gainesville, Florida, orientation uncertain.</li>
+</ol>
+
+<p><span class="pagenum"><a name="Page_192" id="Page_192">[Pg
+192]</a></span></p>
+
+<p style="margin-bottom:2em;"><i>(Microtus) provectus</i> (the last three are probably insular
+derivatives of <i>M. pennsylvanicus</i>), <i>M. (Microtus)
+fulviventer</i> (perhaps derived from the same stock as <i>Microtus
+mexicanus</i>), <i>M. (Microtus) xanthognathus</i> (perhaps related to
+<i>Microtus chrotorrhinus</i>), <i>M. (Microtus) coronarius</i>, and
+<i>M. (Pedomys) ludovicianus</i>.</p>
+
+<table>
+	<tr>
+		<th class="smcap" colspan="2">Species of Which Bacula Were Examined</th>
+	</tr>
+	<tr>
+		<td class="left">Subfamily: Microtinae</td>
+		<td class="right">Number of Specimens</td>
+	</tr>
+	<tr>
+		<td class="bump1" colspan="2">Tribe: Lemmi</td>
+	</tr>
+	<tr>
+		<td class="bump2"><i>Dicrostonyx groenlandicus</i> (Traill)</td>
+		<td class="center">4</td>
+	</tr>
+	<tr>
+		<td class="bump2"><i>Lemmus trimucronatus</i> (Richardson)</td>
+		<td class="center">6</td>
+	</tr>
+	<tr>
+		<td class="bump2"><i>Synaptomys cooperi</i> Baird</td>
+		<td class="center">5</td>
+	</tr>
+	<tr>
+		<td class="bump1" colspan="2">Tribe: Microti</td>
+	</tr>
+	<tr>
+		<td class="bump2" colspan="2">Genus: <i>Clethrionomys</i> Tilesius, 1850</td>
+	</tr>
+	<tr>
+		<td class="bump3"><i>Clethrionomys rutilus</i> Pallas</td>
+		<td class="center">4</td>
+	</tr>
+	<tr>
+		<td class="bump3"><i>Clethrionomys gapperi</i> (Vigors)</td>
+		<td class="center">9</td>
+	</tr>
+	<tr>
+		<td class="bump3"><i>Clethrionomys occidentalis</i> (Merriam)</td>
+		<td class="center">1</td>
+	</tr>
+	<tr>
+		<td class="bump3"><i>Clethrionomys glareolus</i> Schreber</td>
+		<td class="center">1</td>
+	</tr>
+	<tr>
+		<td class="bump3"><i>Clethrionomys rufocanus</i> Sundevall</td>
+		<td class="center">1</td>
+	</tr>
+	<tr>
+		<td class="bump2" colspan="2">Genus: <i>Phenacomys</i> Merriam, 1897</td>
+	</tr>
+	<tr>
+		<td class="bump3"><i>Phenacomys intermedius</i> Merriam</td>
+		<td class="center">5</td>
+	</tr>
+	<tr>
+		<td class="bump2" colspan="2">Genus: <i>Ondatra</i> Link, 1795</td>
+	</tr>
+	<tr>
+		<td class="bump3"><i>Ondatra zibethicus</i> (Linnaeus)</td>
+		<td class="center">1</td>
+	</tr>
+	<tr>
+		<td class="bump2" colspan="2">Genus: <i>Microtus</i> Schrank, 1798</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Herpetomys</i>) <i>guatemalensis</i> Merriam</td>
+		<td class="center">3</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Arvicola</i>) <i>richardsoni</i> (DeKay)</td>
+		<td class="center">2</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Chilotus</i>) <i>oregoni</i> (Bachman)</td>
+		<td class="center">3</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Stenocranius</i>) <i>gregalis</i> (Pallas)</td>
+		<td class="center">1</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Stenocranius</i>) <i>miurus</i> Osgood</td>
+		<td class="center">9</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Chionomys</i>) <i>longicaudus</i> (Merriam)</td>
+		<td class="center">6</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Chionomys</i>) <i>nivalis</i> Martins</td>
+		<td class="center">2</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Microtus</i>) <i>arvalis</i> (Pallas)</td>
+		<td class="center">1</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Microtus</i>) <i>orcadensis</i> Millais</td>
+		<td class="center">1</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Microtus</i>) <i>guentheri</i> Danford and Alston</td>
+		<td class="center">1</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Microtus</i>) <i>fortis</i> B&uuml;chner</td>
+		<td class="center">2</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Microtus</i>) <i>montanus</i> (Peale)</td>
+		<td class="center">15</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Microtus</i>) <i>townsendii</i> (Bachman)</td>
+		<td class="center">3</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Microtus</i>) <i>oeconomus</i> (Pallas)</td>
+		<td class="center">10</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Microtus</i>) <i>mexicanus</i> (Saussure)</td>
+		<td class="center">13</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Microtus</i>) <i>californicus</i> (Peale)</td>
+		<td class="center">2</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Microtus</i>) <i>pennsylvanicus</i> (Ord)</td>
+		<td class="center">13</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Microtus</i>) <i>agrestis</i> (Linnaeus)</td>
+		<td class="center">1</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Pedomys</i>) <i>ochrogaster</i> (Wagner)</td>
+		<td class="center">41</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Pitymys</i>) <i>pinetorum</i> (LeConte)</td>
+		<td class="center">2</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Pitymys</i>) <i>parvulus</i> (Howell)</td>
+		<td class="center">1</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Pitymys</i>) <i>quasiater</i> (Coues)</td>
+		<td class="center">5</td>
+	</tr>
+	<tr>
+		<td class="bump3">(<i>Pitymys</i>) <i>fatioi</i> Mottaz</td>
+		<td class="center">1</td>
+	</tr>
+	<tr>
+		<td class="bump2" colspan="2">Genus: <i>Neofiber</i> True, 1884</td>
+	</tr>
+	<tr>
+		<td class="bump3"><i>Neofiber alleni</i> True</td>
+		<td class="center">2</td>
+	</tr>
+	<tr>
+		<td class="bump2" colspan="2">Genus: <i>Lagurus</i> Gloger, 1841</td>
+	</tr>
+	<tr>
+		<td class="bump3"><i>Lagurus curtatus</i> (Cope)</td>
+		<td class="center">7</td>
+	</tr>
+	<tr>
+		<td class="bump4">Total number examined</td>
+		<td class="center">184</td>
+	</tr>
+</table>
+
+
+<p><span class="pagenum"><a name="Page_193" id="Page_193">[Pg
+193]</a></span></p>
+
+<h2>ACCOUNTS OF SPECIES</h2>
+
+<h3>Dicrostonyx groenlandicus (Traill)</h3>
+<p class="center">Figs. 3 and 4</p>
+
+<p>Baculum: stalk elongate, greatest length (3.1 mm.) 2 <sup>1</sup>/<sub>5</sub> to 2&frac12;
+times greatest breadth, and 4&frac12; times greatest depth; digitate
+processes usually cartilaginous, occasionally lateral processes partly
+ossified; basal tuberosities weakly to moderately developed, medially
+confluent; posterior profile in dorsal view rounded with rounded
+posterior apex or shallow notch; dorsal concavity in end-view shallower
+and not so wide as ventral concavity; median constriction approximately
+<sup>2</sup>/<sub>3</sub> greatest depth; ventral part of base in end-view wider than dorsal
+part; shaft straight or slightly curved; base of stalk placed dorsally
+relative to axis of shaft; stalk spatulate, sometimes with distal
+enlargement; at mid-point stalk wider than high; lateral profile in
+dorsal view sloping gradually without abrupt curvature anterior to point
+of greatest width.</p>
+
+<p>The baculum of <i>Dicrostonyx torquatus</i> figured by Ognev
+(1948:476) agrees with that of <i>D. groenlandicus</i> in shape of stalk,
+and in lateral digitate processes that are small relative to size of
+median process; but differs in more elongate, terminally enlarged, bulbar
+shape of median process. None of my specimens showed ossification in the
+lateral processes, observed by Hamilton (1946:381) in <i>Dicrostonyx
+rubricatus richardsoni</i> [ = <i>D. groenlandicus richardsoni</i>]. In
+all of my specimens the cartilaginous median process was larger than that
+figured by Hamilton, or by Dearden (1958:542).</p>
+
+<p><i>Specimens examined</i>: Four from; Point Barrow, Alaska, 52524
+(Barrow Village), 67264 (died in captivity); Brooks Range, Alaska, 50536
+(Wahoo Lake, 69&deg;08', 146&deg;58'), 50539 (Porcupine Lake, 68&deg;51'57",
+146&deg;29'50", 3140 ft.).</p>
+
+
+<h3>Lemmus trimucronatus (Richardson)</h3>
+<p class="center">Fig. 2</p>
+
+<p>Baculum: Stalk heavy, broad, greatest length (2.8 mm.) in mature
+individuals (Fig. 2) as little as 1<sup>1</sup>/<sub>3</sub> times
+greatest breadth, greatest length no less than 2<sup>2</sup>/<sub>3</sub> times greatest depth
+of base; three ossified processes, median one from as long as to &frac12;
+longer than the lateral processes, and approximately
+<sup>2</sup>/<sub>3</sub> wider and twice as deep as lateral processes;
+length of median process almost 3&frac12; times its breadth,
+approximately &frac12; length of stalk; basal fossae broadly confluent;
+posterior profile in dorsal view evenly rounded; in end-view ventral
+concavity deeper than dorsal concavity, constriction as little as
+&frac12; greatest depth in mature specimens; shaft straight, bluntly
+rounded, or slightly decurved and laterally inflated terminally; lateral
+profile in dorsal view a gradual slope from widest point of stalk
+anteriorly onto shaft; in younger individuals stalk slenderer, otherwise
+as described above.</p>
+
+<p>Five specimens examined by me differ from one figured and described by
+Hamilton (1946:379) in that stalk is better developed, larger relative to
+size of processes, length of stalk in my specimen (Fig. 2) 2.8 as opposed
+to 2.1 mm. in Hamilton's specimen; median process shorter, 1.5 as opposed
+to 1.8 mm., proximal end rounded rather than concave, not partially
+enclosing tip of shaft; proportion of and relative sizes of median and
+lateral processes approximately same as in Hamilton's <i>Lemmus
+helvolus</i> [= <i>Lemmus trimucronatus helvolus</i>].
+
+<span class="pagenum"><a name="Page_194" id="Page_194">[Pg
+194]</a></span>
+
+A specimen figured by Dearden (1958:542) has a basally trilobed median
+process.</p>
+
+<p>The baculum of the Asiatic <i>Lemmus lemmus</i> figured by Ognev
+(1948:413) agrees with my specimens in the ossification of three
+processes, the relative sizes of these processes to each other and to the
+stalk, the well-developed base of the stalk and heavy bluntly rounded
+shaft; the baculum of <i>Lemmus lemmus</i> differs in greater
+anterolateral extent of basal tuberosities, in proximal notch seemingly
+separating these tuberosities, and in median process being slenderer.</p>
+
+<p><i>Specimens examined</i>: Five, of two subspecies; <i>Lemmus
+trimucronatus alascensis</i>, Point Barrow, Alaska, numbers 50591, 50678,
+50731, 50758; <i>Lemmus trimucronatus subarcticus</i>, Wahoo Lake,
+69&deg;08', 146&deg;58', 2350 ft., Brooks Range, Alaska, 50948.</p>
+
+
+<h3>Synaptomys cooperi Baird</h3>
+<p class="center">Figs. 5 and 6</p>
+
+<p>Baculum: Stalk elongate, greatest length (2.7 to 2.8 mm.) 2
+<sup>1</sup>/<sub>3</sub> to 2&frac12; times greatest breadth, 4 to 5
+times greatest depth; three processes ossified or lateral processes
+unossified, ossifications relatively small (in 78380, median ossification
+less than &frac14; as large as lateral ossifications although median
+cartilaginous process is larger), length of median process
+<sup>1</sup>/<sub>5</sub> to <sup>1</sup>/<sub>6</sub> of length of
+stalk, cartilaginous part of median process larger; posterior profile in
+dorsal view convex throughout or bilobate; tuberosities moderately
+developed, deflected dorsal to axis of shaft; in end-view medial
+construction <sup>3</sup>/<sub>5</sub> greatest depth of tuberosities;
+shaft tapered from point of greatest width, slightly inflated
+terminally.</p>
+
+<p>The specimen (KU 13716) figured by Hibbard and Rinker (1942:29) has
+been restudied. It was first cleared and stained to soften the dry
+cartilage binding the digital processes together and to differentiate
+bone and cartilage. The lateral processes are small and cartilaginous
+(Fig. 6) and seem intact. The differences between this specimen and
+others examined by Hamilton (1946:381), Dearden (1958:542), and myself,
+namely the relatively larger median ossification, the absence of
+ossification in lateral processes, and the distinctly bilobate base and
+larger size, may represent geographic differences, or individual
+variation. The proportions of length, width, and depth of the stalk, and
+the appearance in lateral view do not differ greatly from others examined
+by Hamilton, by Dearden (1958:546), and by me.</p>
+
+<p><i>Specimens examined</i>: Five, representing four subspecies; <i>S.
+cooperi gossii</i>, 6 mi. N Midway, Holt Co., Nebraska 78379, 78380;
+<i>S. cooperi relictus</i>, 5 mi. N, 2 mi. W Parks, Dundy Co., Nebraska,
+72601 (immature); <i>S. cooperi saturatus</i>, 3 mi. S Demotte, Jasper
+Co., Indiana, 3-C-454, collection of W. B. Quay; <i>S. cooperi
+paludis</i>, Meade County State Park, Kansas, 13716.</p>
+
+
+<h3>Clethrionomys rutilus Pallas</h3>
+<p class="center">Fig. 11</p>
+
+<p>Baculum: Stalk elongate, and proximally enlarged, greatest length (2.7
+mm.) 2 times greatest breadth; less than 4 times greatest depth; three
+well-developed ossified processes; length of stalk 2<sup>1</sup>/<sub>3</sub> times length of median process; median process
+with basal (and ventral) protuberence and lateral lobes, arched in
+dorsoventral plane; lateral processes as large as median process,
+flattened distally, having ventromedial vane on distal half; basal
+tuberosities of stalk well developed, medially confluent; posterior
+profile in dorsal view trilobate or convex
+
+<span class="pagenum"><a name="Page_195" id="Page_195">[Pg
+195]</a></span>
+
+throughout with rounded posterior apex; dorsal concavity well developed,
+ventral surface but slightly concave, medial constriction of base as
+little as &frac12; greatest depth; shaft straight, slender, at mid-point
+of stalk but slightly wider than high; basal tuberosities largely dorsal
+to axis of shaft in lateral view; lateral profile in dorsal view with an
+abrupt curvature separating the gently sloping sides of the shaft from
+the basal part at its greatest breadth.</p>
+
+<p>The specimen of <i>Clethrionomys rutilus</i> figured by Ognev
+(1950:120) is essentially like the North American specimens examined by
+me in the relative sizes of the ossifications and the general shape of
+the stalk.</p>
+
+<p><i>Specimens examined</i>: Four, of one subspecies; <i>C. r.
+dawsoni</i>, west bank Gakona River, 1700 ft., 5 mi. NNE Gulkana, Alaska,
+42865, 42866; SW end Dezadeash Lake, 2400 ft., Yukon Territory, 42910,
+42921.</p>
+
+
+<h3>Clethrionomys gapperi (Vigors)</h3>
+<p class="center">Fig. 10</p>
+
+<p>Baculum: Stalk elongate, greatest length (2.8 mm.) 1&frac34; times
+greatest breadth, and 3&frac34; times greatest depth; proximally
+enlarged, greatest depth &frac12; greatest breadth; three well-developed
+ossified processes; length of stalk 2 <sup>1</sup>/<sub>3</sub> times
+length of median process; median process arched in dorsoventral plane,
+with basiventral protuberence or spine and lateral lobes; lateral
+processes as large as median process, flattened distally, arched; basal
+tuberosities of stalk well developed, medially confluent; posterior
+profile in dorsal view trilobate or convex throughout with a rounded
+posterior apex; dorsal concavity well developed, ventral surface but
+slightly concave, or in some cases slightly convex; medial constriction
+of base <sup>3</sup>/<sub>5</sub> greatest depth; shaft straight,
+slender, at mid-point of stalk twice as wide as high; basal tuberosities
+dorsally placed relative to axis of shaft; lateral profile in dorsal view
+abruptly curved anterior to point of greatest width; slender stalk
+distinct from angular enlarged base.</p>
+
+<p>The most noticeable difference between the baculum of <i>C.
+rutilus</i> and <i>C. gapperi</i> is size. The proportions of the four
+ossifications are approximately the same. Ventral vanes on the lateral
+processes are not developed in <i>C. gapperi</i>. <i>C. gapperi</i> and
+<i>C. rutilus</i> are more nearly alike in their bacula than any other
+two species of <i>Clethrionomys</i> examined. <i>Clethrionomys
+occidentalis</i>, the other New World species, is also much like <i>C.
+gapperi</i> and <i>C. rutilus</i>. The differences are of a magnitude
+comparable to those between the bacula in subspecies of <i>Microtus
+montanus</i> (Figs. 19-21) for example, or in subspecies of <i>Lagurus
+curtatus</i> (Dearden, 1958:542).</p>
+
+<p><i>Specimens examined</i>: Nine, of two subspecies; <i>Clethrionomys
+gapperi athabascae</i>, British Columbia, 42922 (Indian Creek, Mile Post
+234 of Alaskan Highway), 64281 (West bank Racing River, 89 mi. W Muskwa),
+64287 (North bank Tetsa River, 56 mi. W, 11 mi. S Muskwa), 64290 (44 mi.
+W, 9 mi. S Muskwa), 64310 (32 mi. W, 2 mi. S Muskwa); <i>Clethrionomys
+gapperi galei</i>, 31 mi. N Pinedale, Sublette Co., Wyoming, 42108; Grand
+Mesa, Delta Co., Colorado, 60014 and 60015 (5&frac12; mi. E, 12 mi. S
+Collbran), 60022 (8 mi. E, 1/2 mi. S Skyway).</p>
+
+
+<h3>Clethrionomys occidentalis (Merriam)</h3>
+<p class="center">Fig. 12</p>
+
+<p>Baculum: Stalk elongate, greatest length (2.8 mm.) 2&frac12; times
+greatest breadth, 6 times greatest depth; three well-developed ossified
+processes; median process larger than lateral processes, &frac12; the
+length of stalk, curved, basally
+
+<span class="pagenum"><a name="Page_196" id="Page_196">[Pg
+196]</a></span>
+
+broad, ventrally keeled, trilobate posteriorly; lateral ossifications
+large, flattened distally, curved; posterior profile of stalk posteriorly
+slightly emarginate, thus bilobate in outline; in end-view dorsal
+concavity deeper than ventral, constriction less than &frac12; greatest
+depth, tuberosities confluent, visible in dorsal view at each side; shaft
+slender, especially in depth, straight; at mid-point of stalk almost
+twice as wide as deep, slight terminal inflation.</p>
+
+<p>The general proportions of the stalk and the relatively large,
+uniquely shaped processes, are characteristic of most specimens of the
+genus <i>Clethrionomys</i> examined.</p>
+
+<p><i>Specimen examined</i>: <i>C. occidentalis californicus</i>, one
+from Mary's Peak, Benton Co., Oregon, 30, F. W. Sturges' collection.</p>
+
+
+<h3>Clethrionomys glareolus Schreber</h3>
+<p class="center">Fig. 13</p>
+
+<p>Baculum: Stalk elongate, greatest length (2.9 mm.) twice the greatest
+breadth in the specimen examined, flattened proximally, greatest length
+almost 6 times greatest depth of base; three well-developed ossified
+processes; median process arched in a dorsoventral plane, with basal
+notch and lateral lobes; lateral processes as long as median process,
+bowed in dorsal view, flattened distally, with ventromedial vane; basal
+tuberosities of stalk weakly developed, medially confluent; posterior
+profile in dorsal view evenly rounded; in end-view dorsal concavity
+shallow in comparison to most species but deeper than ventral concavity,
+constriction &frac34; greatest depth; shaft straight, at mid-point
+slightly wider than high, elongate, widest point of stalk less than
+&frac14; of total length from proximal end, slight lateral inflation at
+tip; lateral profile in dorsal view sloping at first abruptly and then
+gradually from widest point of stalk anteriorly onto shaft.</p>
+
+<p>The specimen of <i>Clethrionomys glareolus</i> figured by Ognev
+(1950:31) in dorsal view as I interpret it, resembles my specimen in the
+rounded base; in the elongate, distally inflated shaft; in the initially
+abrupt slope of the lateral profile in dorsal view from the greatest
+width of stalk anteriorly; and in the presence of three well ossified
+processes. Ognev's specimen differs from mine in the median process being
+more elongate relative to its width, and rounded proximally, lacking
+lateral lobes and basal notch; in lateral processes being less curved; in
+the greater terminal inflation of the shaft; and in the closer
+approximation of the terminal processes to the shaft. The baculum of
+<i>Clethrionomys glareolus</i> as described and figured by Didier
+(1954:243-244) resembles my specimen in general proportions, but is more
+pointed proximally and more curved in dorsoventral plane. Didier states
+that the baculum is rather variable in form in this species, in different
+regions, but that a large number of specimens must be examined to assess
+the geographic nature of this variation.</p>
+
+<p><i>Specimen examined</i>: One from Zermatt, Valais, Switzerland,
+67100.</p>
+
+
+<h3>Clethrionomys rufocanus Sundevall</h3>
+<p class="center">Fig. 9</p>
+
+<p>Baculum: Base of stalk broad but relatively flattened dorsoventrally,
+greatest length (3.2 mm.) less than 1&frac12; greatest width, 4 times
+greatest depth; three well-developed ossified processes; median process
+arched in dorsoventral plane, having basal notch and lateral lobes;
+lateral processes as long as median process,
+
+<span class="pagenum"><a name="Page_197" id="Page_197">[Pg
+197]</a></span>
+
+flattened distally, with ventromedial vane; basal tuberosities of stalk
+weakly developed, medially confluent; posterior profile in dorsal view
+convex with rounded posterior apex; dorsal surface of base almost flat,
+ventral concavity broad and shallow; constriction &frac34; greatest depth
+(not including an unusual irregularity on the ventral surface of the
+base); shaft straight, at mid-point of stalk distinctly wider than high,
+slender at distal end, widest point of stalk almost
+<sup>1</sup>/<sub>3</sub> of total length from proximal end, tip of shaft
+rounded; lateral profile in dorsal view gradually sloping from widest
+point anteriorly onto shaft.</p>
+
+<p>The specimen of <i>Clethrionomys rufocanus</i> figured by Ognev
+(1950:97) resembles my specimen in the presence of three well ossified
+processes. Ognev's specimen differs however in the lack of a proximal
+notch on the median process, the lesser proportion of the stalk included
+in the basal enlargement, the more posterior position of the point of
+greatest width, and the presence of a concavity in the posterior profile
+of the stalk in dorsal view. These differences in the stalk may be owing
+to a difference in age (my specimen perhaps being older).</p>
+
+<p><i>Specimen examined</i>: One from 1 mi. NW Oho-ri, 6 M., Korea,
+60438.</p>
+
+
+<h3>Phenacomys intermedius Merriam</h3>
+<p class="center">Figs. 7 and 8</p>
+
+<p>Baculum: Stalk slender, greatest length (2.9 mm.) 2&frac14; to
+2&frac12; times greatest breadth, 4 times greatest depth; three
+well-developed ossified processes, median one almost &frac12; length of
+stalk, curved, broad basally and slightly larger in all dimensions than
+either lateral process; lateral processes flattened distally, curved;
+base of stalk well developed, basal tuberosities medially confluent or
+separated by medial emargination, posterolateral faces flattened or
+rough; emarginations in the four adults examined; posterior profile in
+dorsal view bluntly pointed or flattened except for emargination
+posterially, abruptly curved at point of greatest width; shaft arising
+broadly from distal side of base of stalk; in end-view hour-glass shaped,
+medial constriction pronounced, both dorsal and ventral concavities deep;
+shaft having relatively straight but distally convergent sides; at
+mid-point of stalk, 1 to 1&frac12; times as wide as deep; tip bluntly
+rounded, or slightly inflated.</p>
+
+<p>The specimens from Quebec differ from the one from Wyoming in smaller
+size, relatively smaller lateral digital processes, larger more medial
+basal emargination, and slender shafts. The baculum of <i>Phenacomys
+intermedius</i> differs much from that of <i>Phenacomys longicaudus</i>,
+described by Hamilton (1946:381) and by Dearden (1958:547). Dearden
+states that the three bacula examined by him of <i>Phenacomys
+longicaudus</i> differ markedly from the specimen described by Hamilton.
+It seems to me that in major features the resemblance is greater between
+the specimens of <i>Phenacomys longicaudus</i> examined by these two
+authors than between their specimens and specimens of other microtines,
+including <i>Phenacomys intermedius</i>. Neither Hamilton nor Dearden
+record the exact localities of capture, the collections in which the
+specimens are deposited, or the catalogue numbers of specimens.
+Consequently verification of identifications and observations is
+difficult.</p>
+
+<p><i>Specimens examined</i>: Five, of two subspecies; <i>P. intermedius
+intermedius</i>, 5.4 mi. S Moran, Teton Co., Wyoming, 3-C-309, collection
+of W. B. Quay; <i>P. intermedius celatus</i>, four (including one
+immature specimen) from Authiernord,
+
+<span class="pagenum"><a name="Page_198" id="Page_198">[Pg
+198]</a></span>
+
+Abitibi-ouest Co., Quebec, specimens in collection of Bristol Foster
+designated by numbers 2041-2044 of S. Anderson's field catalogue. Smith
+and Foster (1957:107) were of the view that <i>Phenacomys ungava</i>
+(including the above specimens from Quebec) may be specifically distinct
+from <i>Phenacomys intermedius</i>.</p>
+
+
+<h3>Ondatra zibethicus (Linnaeus)</h3>
+<p class="center">Not figured</p>
+
+<p>Baculum: In the single specimen examined, less mature than that
+figured by Hamilton (1946:384), the digitate processes are cartilaginous,
+the basal tuberosities are less well developed, and the shaft is
+slenderer throughout. The cartilaginous processes are of the same
+proportions as ossified processes in the figure mentioned. The shaft is
+also convex ventrally in lateral profile. The view of the side here
+considered to be anatomically the ventral side (adjacent to the urethra)
+is labelled dorsal view in Hamilton's specimen.</p>
+
+<p><i>Specimen examined</i>: One, from Reserve, Brown Co., Kansas, 72405.</p>
+
+
+<h3>Microtus (Herpetomys) guatemalensis Merriam</h3>
+<p class="center">Figs. 42 and 43</p>
+
+<p>Baculum: Stalk moderately elongate, greatest length (3.5 mm.)
+2<sup>1</sup>/<sub>3</sub> times greatest breadth, spatulate, flattened
+throughout, greatest thickness <sup>1</sup>/<sub>3</sub> millimeter;
+three ossified processes; median process having three cornered base,
+curved dorsally, wider than high, &frac14; to <sup>1</sup>/<sub>5</sub>
+greatest length of stalk; each lateral process bent at middle, as long as
+median process, compressed laterally; base of stalk curved dorsally,
+tuberosities marginal, hence narrow, lateral excavations of tuberous
+margin not confluent medially; in end-view ventral concavity broad, no
+dorsal concavity, medial constriction but slightly less than greatest
+thickness (not depth); shaft wider than high throughout, at mid-point
+more than 3 times as wide as high; tip of shaft slightly inflated both
+laterally and dorsoventrally; lateral profile gradually sloping
+anteriorly from widest point of stalk.</p>
+
+<p>Specimen number 65921 (Fig. 43) differs from number 65895 (Fig. 42)
+described above. Terminus of shaft of number 65921 has lateral lobes from
+which arise lateral cartilaginous processes; median terminal ossification
+irregular in shape, smaller, imbedded in terminally bilobate cartilage.
+In the spatulate flattened stalk these two specimens are much alike. An
+immature specimen, number 65908, is smaller (length of stalk 2.6 mm.)
+also flattened and spatulate, has the terminal processes cartilaginous,
+the lateral processes bent medially, and proportions as in the adult.</p>
+
+<p>The baculum shows no noteworthy resemblance to that of any other
+species of North American <i>Microtus</i>; on the other hand the
+differences between <i>M. guatemalensis</i> and some other species are no
+greater than the differences between certain species included in the
+subgenus <i>Microtus</i>. The baculum neither strengthens nor weakens the
+case for subgeneric rank for <i>M. (Herpetomys) guatemalensis</i>.</p>
+
+<p><i>Specimens examined</i>: Three from Guatemala; 65895 (2 mi. S San
+Juan Ixcoy), 65908, (3-1/2 mi. SW San Juan Ixcoy), 65921 (10 mi. E, 4 mi.
+S Totonicap&aacute;n).</p>
+
+<p><span class="pagenum"><a name="Page_199" id="Page_199">[Pg
+199]</a></span></p>
+
+
+<h3>Microtus (Arvicola) richardsoni (DeKay)</h3>
+<p class="center">Figs. 38 and 39</p>
+
+<p>Baculum: Stalk broad, greatest length (3.7 to 4.3 mm.) 1&frac12; times
+greatest breadth, relatively flattened, greatest depth
+<sup>1</sup>/<sub>3</sub> greatest breadth; single median ossified
+process, in smaller of two specimens this ossification incomplete and of
+unusual shape (Fig. 39); length of stalk 4 times length of median
+process; concavities of basal tuberosities medially confluent,
+constriction less than &frac12; greatest depth; widest point of shaft
+less than &frac14; length of shaft from posteriormost point; shaft wider
+than high except at distal end that is inflated dorsally and sometimes
+laterally; both ventral and dorsal concavities of base of stalk broad and
+moderately deep; posterior profile in dorsal view evenly rounded or
+having marginal notch.</p>
+
+<p>In the absence of ossified lateral processes my two specimens differ
+from bacula of <i>Microtus (Arvicola) terrestris</i> figured by Didier
+(1943:79, 1954:245, 247, 248) and by Ognev (1950:591). The median process
+relative to the size of the shaft is smaller, and the shaft relative to
+its length is wider in <i>M. richardsoni</i> than in <i>M.
+terrestris</i>. The stalk of <i>M. (Arvicola) amphibius</i> figured by
+Didier is like that of <i>M. richardsoni</i> in its greater breadth and
+median notch on posterior border.</p>
+
+<p>The relationship of the New World water rat, <i>M. richardsoni</i>, to
+the Old World water rats (genus <i>Arvicola</i> of some European authors)
+is uncertain. Miller (1896:66) placed all of them in the subgenus
+<i>Arvicola</i>. Subsequent authors, stressing differences in the teeth,
+have placed <i>M. richardsoni</i> in the subgenus <i>Aulacomys</i> of
+Rhoads. Zimmerman (1955) has shown that teeth in some <i>Arvicola</i>
+approach the more complex pattern of <i>M. richardsoni</i>. He argues
+also that <i>Arvicola</i> is generically distinct from <i>Microtus</i> on
+the grounds that the two groups have separate origins, <i>Arvicola</i>
+having descended from the genus <i>Mimomys</i> and <i>Microtus</i> from
+some other group of microtines. This argument also was advanced by Hinton
+(1926:47-48). Pending further studies of the possible polyphyletic origin
+of other subgenera of the genus <i>Microtus</i>, I refer both <i>M.
+richardsoni</i> and <i>M. terrestris</i> to the subgenus <i>Arvicola</i>.</p>
+
+<p>The evidence afforded by the bacula available is not conclusive as to
+relations of Old World and New World water rats. No general agreement on
+the number of species in this Palaearctic group has been reached, and
+bacula of only three or four of the numerous Old World subspecies have
+been figured. I have examined none.</p>
+
+<p><i>Specimens examined</i>: Two, from Wyoming; 42454 (31 mi. N
+Pinedale, 8025 ft., Sublette Co.), 37903 (23-1/2 mi. S, 5 mi. W Lander,
+8600 ft., Fremont Co.).</p>
+
+
+<h3>Microtus (Chilotus) oregoni (Bachman)</h3>
+<p class="center">Fig. 45</p>
+
+<p>Baculum: Stalk broad, greatest length (2.2 mm.) 1&frac34; times
+greatest breadth, 3&frac12; times greatest depth; three well-developed
+ossified processes; median process <sup>2</sup>/<sub>5</sub> length of
+stalk, rounded or tapered terminally, proximal end opposed to tip of
+stalk and flattened obliquely; lateral processes
+<sup>2</sup>/<sub>3</sub> length of median process, deeper than wide,
+curved; tuberosities of stalk well developed, confluent medially, visible
+in dorsal view; in end-view dorsal concavity narrow, moderately
+
+<span class="pagenum"><a name="Page_200" id="Page_200">[Pg
+200]</a></span>
+
+deep, rounded, ventral concavity wide, deep, flattened; base wider
+ventrally than dorsally; shaft tapering more or less uniformly,
+terminally inflated.</p>
+
+<p>In the relative sizes, to each other and to the stalk, of the three
+digitate ossifications <i>M. oregoni</i> resembles closely the Old World
+representative of the same subgenus, <i>M. (Chilotus) socialis</i>, as
+figured by Argyropulo (1933b:181). In <i>M. oregoni</i> the greatest
+width of the baculum is more proximal on the stalk than in the <i>M.
+socialis</i> figured by Argyropulo but closely resembles the baculum of
+the <i>M. socialis</i> figured by Didier (1954:242). In possessing a
+shallow emargination in the base of the stalk and in possessing a median
+process that is smaller than the lateral processes, <i>M. socialis</i>,
+as figured by Didier, differs from <i>M. oregoni</i>. The baculum figured
+by Argyropulo (<i>loc. cit.</i>) of <i>Sumeriomys colchicus
+schidlovskii</i> [ = <i>Microtus (Chilotus) socialis schidlovskii</i>
+according to Ognev, 1950:392] differs from other <i>Chilotus</i> that
+have been studied in having an unusually elongate median process and a
+more distal placement of the widest part of the stalk.</p>
+
+<p><i>Specimens examined</i>: Three, of the subspecies <i>M. oregoni
+oregoni</i>, from 5 mi. N Orick, Humboldt Co., California, 3-C-248,
+collection of W. B. Quay; from Mary's Peak, Benton Co., Oregon, 66,
+collection of F. W. Sturges; and from Sec. 3, T. 11S, R. 5W, Benton Co.,
+Oregon, 79183.</p>
+
+
+<h3>Microtus (Stenocranius) gregalis (Pallas)</h3>
+<p class="center">Fig. 34</p>
+
+<p>Baculum: Length of stalk (2.4 mm.) 1&frac34;, times greatest breadth,
+4<sup>1</sup>/<sub>3</sub> times greatest depth; median ossified process
+well developed, more than <sup>1</sup>/<sub>3</sub> length of stalk,
+higher than wide, slightly bowed, closely appressed to terminus of shaft;
+basal tuberosities of stalk moderately developed, confluent medially,
+posterior profile of medial apex rounded in dorsal view, lateral
+indentations present, hence trilobate outline; in proximal end-view base
+wider ventrally, ventral concavity broader than dorsal concavity but of
+equal depth, medial constriction <sup>2</sup>/<sub>3</sub> greatest
+depth; shaft slender in distal part, inflated terminally, and wider than
+high at mid-point of stalk; lateral profile a smooth slope of gradually
+decreasing curvature from point of greatest width to near distal end.</p>
+
+<p>The baculum of this species figured by Ognev (1950:461) differs in
+having lateral ossified processes, and a more rounded base of the stalk.
+Resemblance to the New World <i>Stenocranius</i> is discussed below.</p>
+
+<p><i>Specimen examined</i>: One from "Eastern Europe," 8059.</p>
+
+
+<h3>Microtus (Stenocranius) miurus Osgood</h3>
+<p class="center">Figs. 32 and 33</p>
+
+<p>Baculum: Length of stalk (2.8 mm.) 1&frac12; times greatest breadth,
+3&frac12; times greatest depth; median process ossified,
+<sup>2</sup>/<sub>5</sub> to <sup>3</sup>/<sub>5</sub> length of stalk,
+laterally compressed, sometimes arched in dorsoventral plane; lateral
+processes cartilaginous, slender; basal tuberosities well developed,
+averaging less enlarged than shown in Figure 32, but more angular in
+lateral outline than shown in Figure 33; tuberosities confluent
+posteriorly; posterior profile smoothly rounded to trilobate, curvature
+at point of greatest breadth usually acute; in proximal end-view base
+wider dorsally, deep dorsal concavity, shallow ventral concavity, medial
+constriction <sup>3</sup>/<sub>5</sub> of greatest depth; shaft slender
+anteriorly, at mid-point of stalk
+
+<span class="pagenum"><a name="Page_201" id="Page_201">[Pg
+201]</a></span>
+
+twice as wide as high, at tip higher than wide, laterally inflated;
+lateral profile in most specimens abruptly curved anterior to point of
+greatest breadth.</p>
+
+<p>The single specimen of the Old World <i>M. (Stenocranius) gregalis</i>
+examined resembles the New World <i>M. (Stenocranius) miurus</i> in the
+angular lateral profile at the point of greatest breadth of the stalk,
+slender shaft in comparison to broad base of stalk, and presence of a
+single well-developed laterally compressed median process. The base of
+the stalk in the baculum of <i>M. gregalis</i> is less well developed and
+smaller than in the baculum of <i>M. miurus</i>.</p>
+
+<p><i>Specimens examined</i>: Nine, all of the subspecies <i>Microtus
+miurus muriei</i>, from the Brooks Range, Alaska; 51077 (Lake Schrader,
+145&deg;09'50", 69&deg;24'28", 2900 ft., Romanzof Mts.); 51151, 51152,
+51154, 51164, 51166, 51169 (last 6 from Wahoo Lake, 69&deg;08',
+146&deg;58', 2350 ft.); 51210, 51213 (last 2 from Porcupine Lake,
+68&deg;51'57", 146&deg;29'50", 3140 ft.).</p>
+
+
+<h3>Microtus (Chionomys) nivalis Martins</h3>
+<p class="center">Fig. 47</p>
+
+<p>Baculum: Greatest length of stalk (2.7 mm.) 2&frac14; times greatest
+breadth, 4&frac12; times greatest depth; three digitate processes,
+lateral processes mostly cartilaginous in single adult examined; median
+process well ossified, approximately <sup>1</sup>/<sub>3</sub> length of
+stalk, basally notched, not arched, laterally compressed distally; base
+of stalk broad and flat, basal tuberosities well developed, separate;
+posterior profile in dorsal view rounded, convex except for medial notch
+separating tuberosities; dorsal and ventral concavities deep, broad,
+equal; medial constriction less than &frac12; greatest depth; in dorsal
+view shaft tapering gradually from widest point, terminally rounded; at
+mid-point of stalk almost twice as wide as high.</p>
+
+<p>In the elongate, largely cartilaginous lateral processes of the
+baculum, the specimen described above resembles <i>M. longicaudus</i>.
+The size of the median process in comparison to the size of the stalk is
+also the same. The lateral processes have larger ossifications and the
+base of the stalk is more robust in <i>M. longicaudus</i> than in <i>M.
+nivalis</i>.</p>
+
+<p>The well ossified lateral processes and enlarged base of Didier's
+(1954:240) specimen suggest that it is of a more mature individual than
+the one described above. These specimens of <i>M. nivalis</i>, as well as
+the specimens of <i>M. longicaudus</i>, exhibit dorso-ventral flattening
+of the mid-part of the base of the stalk.</p>
+
+<p>The baculum of a specimen from Switzerland is weakly developed, of
+small size (shaft 2.0 mm. in length), slender, thin, spatulate, and
+terminally inflated. Digital processes were not observed, perhaps owing
+to excessive maceration in preparation. The general appearance of the
+baculum is that of an immature individual, although the animal was not
+small (165 mm. total length in preservative).</p>
+
+<p><i>Specimens examined</i>: Two <i>Microtus nivalis nivalis</i>;
+Zermatt, Valais, Switzerland, 67105; Wetterstein, Germany, 65127.</p>
+
+
+<h3>Microtus (Chionomys) longicaudus (Merriam)</h3>
+<p class="center">Fig. 48</p>
+
+<p>Baculum: Base of stalk well developed, greatest length (3 mm.)
+1&frac34; times greatest breadth, 3<sup>2</sup>/<sub>3</sub> times
+greatest depth; three ossified processes; base of median process rounded;
+median process slightly curved in dorsoventral plane, in length almost
+<sup>1</sup>/<sub>3</sub> greatest length of stalk; ossifications in
+lateral processes
+
+<span class="pagenum"><a name="Page_202" id="Page_202">[Pg
+202]</a></span>
+
+variable in size, frequently widely separated from shaft by cartilage,
+rarely as large as median ossification; basal tuberosities usually
+well-developed, medially confluent; profile of base in dorsal view
+trilobate or irregularly convex throughout; constriction &frac12;
+greatest depth; shaft relatively straight or slightly bowed ventrally or
+dorsally, shaft at mid-point of stalk wider than high; tip of shaft
+laterally inflated; widest point of stalk approximately &frac14; length
+of stalk from proximal end; lateral profile in dorsal view tapers
+gradually onto shaft anteriorly from point of greatest width of stalk;
+shaft variable, from slender terminally and nearly parallel sided (Fig.
+48), to broad distally and tapered.</p>
+
+<p>In many of the features that distinguish <i>M. longicaudus</i> (and
+the closely related insular species <i>M. coronarius</i>) from other
+North American <i>Microtus</i>, <i>longicaudus</i> resembles the Old
+World species of the subgenus <i>Chionomys</i> (that is to say, <i>M.
+nivalis</i>, <i>M. gud</i>, and <i>M. roberti</i>). These features are
+medium size, long tail, grayish color, montane habitat, relatively short
+molar tooth-row, moderate sized and unconstricted incisive foramen,
+relatively decurved upper incisors, elongate nasals, relatively broad
+interorbital region without well-developed median ridge, and similar
+chromosomes (Matthey, 1955:178). For these reasons I am here referring
+<i>Microtus longicaudus</i> to the subgenus <i>Chionomys</i>; previously
+it has not been referred to that subgenus.</p>
+
+<p><i>Specimens examined</i>: Six, of three subspecies; <i>Microtus
+longicaudus littoralis</i>, Sullivan Island, Alaska, 42972, 42969; <i>M.
+l. mordax</i>, 3/4 mi. N, 2 mi. W Allenspark, 8400 ft., Boulder Co.,
+Colorado, 50335, 76829; <i>M. l. sierrae</i>, Crane Flat, Mariposa Co.,
+California, 50252, 50253.</p>
+
+
+<h3>Microtus arvalis (Pallas)</h3>
+<p class="center">Fig. 22</p>
+
+<p>Baculum: In the single specimen examined, stalk small, greatest length
+(2.3 mm.) 2<sup>1</sup>/<sub>3</sub> times greatest width, almost 6 times
+greatest depth, flattened proximally; three well-developed digitate
+processes, the median one ossified, the lateral processes cartilaginous;
+median ossification laterally compressed and decurved at tip, bilobate at
+base; basal tuberosities of stalk weakly developed, medially confluent;
+posterior profile in dorsal view evenly rounded; ventral concavity deeper
+and narrower than dorsal concavity, but both comparatively shallow;
+medial constriction <sup>2</sup>/<sub>3</sub> greatest depth; shaft
+straight, at mid-point twice as wide as deep; lateral profile tapering
+from greatest width gradually to parallel sides of distal third of
+stalk.</p>
+
+<p>From the baculum of <i>Microtus arvalis</i> figured by Ognev
+(1950:173), and from the baculum figured by Didier (1954:238) my specimen
+differs in the absence of lateral ossifications in the digitate
+processes, smaller and slenderer median ossification, and weaker base.
+These differences in part may be owing to a difference in age, my
+specimen being the less mature.</p>
+
+<p><i>Specimen examined</i>: One from Vidy, Switzerland, 67101.</p>
+
+
+<h3>Microtus orcadensis Millais</h3>
+<p class="center">Fig. 24</p>
+
+<p>Baculum: In the one specimen examined, stalk broad, greatest length
+(2.6 mm.) 1&frac12; times greatest breadth, 3&frac12; times greatest
+depth; three digitate processes ossified; median process relatively
+broad, in length more than &frac12; length of stalk, triangular in dorsal
+view, with small spurs posterolaterally,
+
+<span class="pagenum"><a name="Page_203" id="Page_203">[Pg
+203]</a></span>
+
+middorsal ridge posteriorly; lateral ossifications slightly curved,
+slenderer, less than &frac12; depth and less than &frac12; transverse
+thickness of median process; basal tuberosities well-developed, confluent
+medially; in end-view base wider dorsally than ventrally, dorsal
+concavity broader and more abruptly curved at mid-point than ventral
+concavity; constriction &frac12; greatest depth; posterior profile in
+dorsal view notched, setting off a posterior shelf; stalk including shaft
+wider than deep throughout, at mid-point width twice depth; lateral
+profile abruptly curved anterior to point of greatest width, sides of
+shaft tapering gradually anteriorly to rounded uninflated tip.</p>
+
+<p>The baculum of this insular species, placed in the "<i>arvalis</i>"
+group by Ellerman (1941:595), resembles the baculum of both <i>Microtus
+agrestis</i> and <i>Microtus guentheri</i> more than it resembles the
+baculum of <i>Microtus arvalis</i>. Similarities in the chromosomes of
+<i>M. arvalis</i> and <i>M. orcadensis</i> were noted by Matthey
+(1953:254, 279), who was of the opinion that <i>M. orcadensis</i> is an
+insular derivative of the <i>arvalis</i>-group.</p>
+
+<p><i>Specimen examined</i>: One from the Orkney Islands, 67106.</p>
+
+
+<h3>Microtus guentheri Danford and Alston</h3>
+<p class="center">Fig. 23</p>
+
+<p>Baculum: In the one specimen examined, stalk broad, greatest length
+(2.9 mm.) 1&frac12; times greatest breadth, 3&frac12; times greatest
+depth; three digitate processes ossified; median process slightly less
+than &frac12; length of stalk, broad, dorsally curved; curved lateral
+ossifications shorter and more slender than median ossification; basal
+tuberosities well developed, angular, confluent across posterior border
+of projecting shelf; in end-view tuberosities projecting ventrolaterally
+from central shelf; dorsal surface at medial constriction flat, ventral
+surface broadly and deeply concave; posterior profile in dorsal view
+trilobate, central lobe formed by posteriorly flattened shelf, surface of
+attachment visible only on lateral lobes; at mid-point stalk almost twice
+as wide as deep, depth of shaft greater than width proximal to inflated
+terminus.</p>
+
+<p><i>Specimen examined</i>: One from Palestine, 67104.</p>
+
+
+<h3>Microtus fortis B&uuml;chner</h3>
+<p class="center">Fig. 25</p>
+
+<p>Baculum: Stalk large, greatest length (3.8 mm.)
+1<sup>4</sup>/<sub>5</sub> times greatest breadth, 4&frac12; times
+greatest depth; three digitate processes ossified; median ossification
+almost <sup>1</sup>/<sub>3</sub> length of stalk; lateral ossifications
+slender, smaller than median ossification; posterior profile of stalk in
+dorsal view trilobate, basal tuberosities well developed, confluent
+medially; in end-view dorsal concavity broader and deeper than ventral
+concavity; medial constriction pronounced (less than &frac12; greatest
+depth); lateral profile at widest point of stalk convex, becoming
+abruptly concave as the flange of the basal tuberosities grades into the
+shaft, then gradually converging to narrowest point
+<sup>1</sup>/<sub>3</sub> of length of stalk from the terminus; stalk
+wider than deep in proximal <sup>2</sup>/<sub>3</sub>, circular in cross
+section in terminal <sup>1</sup>/<sub>3</sub>, slight terminal
+inflation.</p>
+
+<p>A specimen figured by Ognev (1950:297) has the same general
+proportions, slender lateral processes, and proximal placement of the
+point of greatest breadth.</p>
+
+<p><i>Specimens examined</i>: Two from Chipo-ri, Korea, 60443, 63841.</p>
+
+<p><span class="pagenum"><a name="Page_204" id="Page_204">[Pg
+204]</a></span></p>
+
+
+<h3>Microtus montanus (Peale)</h3>
+<p class="center">Figs. 19, 20 and 21</p>
+
+<p>Baculum: Stalk broad, greatest length (varying with subspecies from
+2.3 to 3.1 mm.) 1&frac12; to 1&frac34; times greatest breadth,
+3<sup>1</sup>/<sub>3</sub> to 4<sup>1</sup>/<sub>3</sub> times greatest
+depth; three ossified processes, median one largest, more than twice as
+wide and as deep as shorter, slenderer, lateral processes; median process
+laterally compressed distally except in one specimen in which moderately
+inflated distally, proximally enlarged in some specimens (Fig. 21) and
+<sup>1</sup>/<sub>3</sub> to <sup>2</sup>/<sub>5</sub> length of stalk;
+base broad, posterior profile in dorsal view evenly convex throughout, at
+widest point of stalk abruptly incurved; basal tuberosities moderately to
+strongly developed, medially confluent; in end-view base wider ventrally
+than dorsally, dorsal concavity slightly to much deeper than the nearly
+flattened ventral concavity; medial constriction
+<sup>2</sup>/<sub>3</sub> to <sup>4</sup>/<sub>5</sub> of greatest depth;
+shaft relatively slender, at mid-point of stalk slightly wider than high
+and &frac14; as wide as base of stalk, terminally rounded or slightly
+inflated; lateral profile in dorsal view a gradual curve from point of
+greatest width anteriorly onto shaft.</p>
+
+<p>The different subspecies figured show the essential characteristics of
+the species, differing primarily in size.</p>
+
+<p><i>Specimens examined</i>: Fourteen, of three subspecies; <i>Microtus
+montanus amosus</i>, &frac12; mi. E Soldier Summit, Wasatch Co., Utah,
+62241; <i>M. montanus fusus</i>, La Manga Pass, Conejos Co., Colorado,
+42164; 5 mi. N, 26 mi. W Saguache, 9500 ft., Saguache Co., Colorado,
+42307, 42315; 5 mi. N, 27 mi. W Saguache, 9350 ft., Saguache Co.,
+Colorado, 42308; 5 mi. N, 28 mi. W Saguache, 9325 ft., Saguache Co.,
+Colorado, 42309; 5 mi. S, 24 mi. W Antonito, 9600 ft., Conejos Co.,
+Colorado, 42327, 42330; Prater Canyon, Mesa Verde National Park,
+Montezuma Co., Colorado, 69456, 69457, 69463; <i>Microtus montanus
+nanus</i>, 2 mi. N, 2 mi. W Pocatello, Bannock Co., Idaho, 57470, 57472;
+&frac14; mi. N, 2 mi. W Allenspark, 8400 ft., Boulder Co., Colorado,
+50330.</p>
+
+
+<h3>Microtus townsendii (Bachman)</h3>
+<p class="center">Fig. 41</p>
+
+<p>Baculum: Stalk broad, greatest length (3.0 mm.) 1&frac12; times
+greatest breadth, 4&frac12; times greatest depth; three ossified
+processes, median one largest, deeper and more than twice as wide as
+curved, shorter, compressed lateral processes and more than
+<sup>2</sup>/<sub>5</sub> as long as stalk; base broad, in dorsal view
+posterior profile trilobate, basal tuberosities visible; basal
+tuberosities well developed, medially confluent; in end-view base wider
+ventrally than dorsally, dorsal concavity deeper than ventral concavity;
+medial constriction <sup>3</sup>/<sub>5</sub> of greatest depth; shaft
+broad, at mid-point more than twice as wide as high and
+<sup>1</sup>/<sub>3</sub> as wide as base of stalk, terminally
+rounded.</p>
+
+<p><i>Specimens examined</i>: Three, all <i>M. t. townsendii</i>; Fort
+Lewis, Pierce Co., Washington, 57998, subadult; Sec. 33, T. 11S, R. 5W,
+Benton Co., Oregon, 79186; Sec. 5, T. 12S, R. 4W, Benton Co., Oregon,
+79188.</p>
+
+
+<h3>Microtus oeconomus (Pallas)</h3>
+<p class="center">Fig. 44</p>
+
+<p>Baculum: Stalk broad and flattened, greatest length (3.5 mm.)
+1<sup>2</sup>/<sub>3</sub> to 2 times greatest width, 4 to 5&frac12;
+times greatest depth; three ossified processes, median one largest,
+lateral processes slender, relatively small; length of median process
+<sup>3</sup>/<sub>8</sub> length of stalk; median process decurved,
+dorsoventrally flattened in
+
+<span class="pagenum"><a name="Page_205" id="Page_205">[Pg
+205]</a></span>
+
+some specimens, widened at base; attachment of processes to shaft
+displaced ventrally; base of stalk widened, posterior profile in dorsal
+view usually trilobate, in a few cases rounded, median lobe forming
+posterior shelf, lateral lobes dorsally raised and forming margins of
+lateral tuberosities; in end-view thickness frequently more or less
+uniform throughout central part, broad depression dorsally, ventral
+concavity narrower and shallower (as figured); base, and occasionally
+shaft, flattened, width at mid-point of stalk 2 to 3 times depth,
+narrowest point posterior to terminal inflation of shaft in terminal
+<sup>1</sup>/<sub>3</sub> of shaft.</p>
+
+<p>The baculum of <i>M. oeconomus</i> (Old World) figured by Ognev
+(1950:257) resembles but exceeds that of <i>M. oeconomus</i> (New World)
+in the relatively large median process and slender lateral processes, but
+differs noticeably in the presence of a deep median notch in the base of
+the stalk. A specimen from Hungary is intermediate between Ognev's
+specimen and those from the New World in both size of median process and
+size of lateral processes, and has an unnotched base resembling that in
+Figure 44.</p>
+
+<p><i>Specimens examined</i>: Ten, of three subspecies; <i>M. oeconomus
+gilmorei</i>, Umiat, Alaska, 51354, 51361, 51399, 51408; Lake Schrader,
+Brooks Range, Alaska, 51422; <i>M. o. macfarlani</i>, 5 mi. NNE Gulkana,
+Alaska, 43039, 43041; 20 mi. NE Anchorage, Alaska, 43044; Kelsall Lake,
+British Columbia, 43048; <i>M. o. mehelyi</i>, Kisbalatan, Hungary,
+75159.</p>
+
+
+<h3>Microtus mexicanus (Saussure)</h3>
+<p class="center">Figs. 35 and 36</p>
+
+<p>Baculum: Stalk attenuate, greatest breadth relatively near proximal
+end; greatest length (3.1 to 3.4 mm.) more or less twice greatest
+breadth, 4 to 5 times greatest depth; usually a single process ossified;
+lateral processes relatively small, cartilaginous or (in three specimens,
+63094, 69453, 68019) with small ossifications; median process relatively
+small, sometimes appressed to tip of shaft, in length less than &frac14;
+length of stalk; posterior profile in dorsal view rounded, flattened
+posteriorly, or in some specimens trilobate with angular edges; in
+end-view relative depths of dorsal and ventral concavities variable,
+dorsal usually deeper than ventral; distal end of stalk frequently bowed
+dorsally; shaft slender distally, sometimes slightly inflated terminally,
+or (in one specimen, 63085) near tip small lateral projections that are
+perhaps fused lateral ossifications; lateral profile in dorsal view a
+gradual slope anteriorly from point of greatest width to slender tip.</p>
+
+<p><i>Specimens examined</i>: Thirteen, of four subspecies; <i>Microtus
+mexicanus mexicanus</i>, Las Vigas, Veracruz, 30692; Nevada de Toluca,
+M&eacute;xico, 63101; Valle de Bravo, M&eacute;xico, 63094; <i>Microtus mexicanus
+mogollonensis</i>, Mt. Taylor, Valencia Co., New Mexico, 63298, 76830;
+Park Well, Mesa Verde National Park, Montezuma Co., Colorado, 69448,
+69453; Upper Nutria, McKinley Co., New Mexico, 69997, 70000; <i>Microtus
+mexicanus phaeus</i>, Sierra Patamba, 9000 ft., Michoac&aacute;n, 63085;
+<i>Microtus mexicanus subsimus</i>, 2 mi. E Mesa de Tablas, Coahuila,
+58916; 13 mi. E San Antonio de las Alazanas, Coahuila, 68019, 68021.</p>
+
+
+<h3>Microtus californicus (Peale)</h3>
+<p class="center">Fig. 37</p>
+
+<p>Baculum: Stalk elongate, greatest length (3.0 mm.)
+2<sup>1</sup>/<sub>3</sub> times greatest breadth, 4&frac12; times
+greatest depth; median process ossified, &frac14; length of stalk,
+basally broadened, flattened and shallowly grooved ventrally to fit tip
+of shaft, to which the process is closely appressed; lateral processes
+cartilaginous; ends
+
+<span class="pagenum"><a name="Page_206" id="Page_206">[Pg
+206]</a></span>
+
+of stalk bowed upwardly; posterior profile of base of stalk rounded or
+slightly trilobate if posterolateral concavities form in tuberosities;
+moderate development of tuberosities, in end-view dorsal concavity
+slightly deeper and narrower than ventral concavity, both comparatively
+shallow, median constriction <sup>4</sup>/<sub>5</sub> greatest depth;
+shaft curved, more or less terete at mid-point of stalk, terminally
+inflated dorsally; lateral profile in dorsal view gradually curved from
+point of greatest width anteriorly onto shaft.</p>
+
+<p><i>Specimens examined</i>: Two, of two subspecies; <i>Microtus
+californicus californicus</i>, 1 mi. NE Berkeley, in Contra Costa Co.,
+California, 76828; <i>Microtus californicus mohavensis</i>, &frac12; mi.
+SE Victorville, San Bernardino Co., California, 63745.</p>
+
+
+<h3>Microtus pennsylvanicus (Ord)</h3>
+<p class="center">Figs. 14, 15, 16 and 17</p>
+
+<p>Baculum: Stalk heavy, broad, greatest length (2.2 to 3.0 mm.)
+1<sup>1</sup>/<sub>3</sub> to 1<sup>2</sup>/<sub>3</sub> times greatest
+breadth, up to 3&frac34; times greatest depth; three ossified processes,
+median one largest, usually not twice so deep as lateral ossifications;
+median process usually distinctly widened basally, in length
+approximately &frac12; length of stalk; base broad, frequently angular
+laterally and basally, sometimes bilobate; basal tuberosities well
+developed, medially confluent; in end-view more or less uniformly
+biconvex or ventral surface more flattened than dorsal surface, medial
+constriction &frac12; to <sup>2</sup>/<sub>3</sub> greatest depth; shaft
+relatively heavy, at mid-point stalk almost twice as wide as deep and
+<sup>1</sup>/<sub>3</sub> as wide as base of stalk; shaft terminally
+rounded and sometimes slightly inflated; lateral profile in dorsal view
+abruptly or gradually curved anterior to point of greatest width and then
+gradually curved anteriorly.</p>
+
+<p>Specimens examined averaged slightly smaller and were more variable
+than those described by Hamilton (1946:382). The greater variation may be
+in part geographic, as five subspecies are represented. Lateral processes
+are the last to ossify. One specimen (75082) with well-ossified median
+process lacks any lateral ossification. Four bacula of <i>M.
+pennsylvanicus</i> (locality not specified) studied by Dearden (1958:547)
+agree in general with the description above.</p>
+
+<p>One specimen shows a break, perhaps resulting from injury, in the
+shaft (Fig. 14). One specimen has a posteromedian spine on the median
+digital ossification (Fig. 16). Comparison with <i>M. agrestis</i> is
+included with the description of <i>M. agrestis</i>.</p>
+
+<p><i>Specimens examined</i>: Thirteen, of six subspecies; <i>Microtus
+pennsylvanicus alcorni</i>, 20 mi. NE Anchorage, Alaska, 43043;
+<i>Microtus pennsylvanicus finitus</i>, Laird, Yuma Co., Colorado, 68544;
+<i>Microtus pennsylvanicus modestus</i>, 5 mi. N, 26 mi. W Saguache, 9500
+ft., Saguache Co., Colorado, 42306; 3 mi. N, 16 mi. W Saguache, 8500 ft.,
+Saguache Co., Colorado, 42416, 42417, 42418; 1 mi. S, 2 mi. E Eagle Nest,
+8100 ft., Colfax Co., New Mexico, 42430, 42439; <i>Microtus
+pennsylvanicus pennsylvanicus</i>, 2 mi. S, 3 mi. E Ft. Thompson, 1370
+ft., Buffalo Co., South Dakota, 42379; Vermillion, Clay Co., South
+Dakota, 37070; <i>Microtus pennsylvanicus pullatus</i>, 12 mi. S, 5 mi. E
+Butte, Silver Bow Co., Montana, 57501, 57503; <i>Microtus pennsylvanicus
+uligocola</i>, Muir Springs, 2 mi. N, 2&frac12;mi. W Ft. Morgan, Morgan
+Co., Colorado, 75082.</p>
+
+
+<h3>Microtus agrestis (Linnaeus)</h3>
+<p class="center">Fig. 18</p>
+
+<p>Baculum: Greatest length of stalk (2.9 mm.) twice greatest breadth,
+4&frac12; times greatest depth; stalk well developed, shaft not flattened
+dorsoventrally; large median ossified process, minute lateral
+ossifications in single specimen
+
+<span class="pagenum"><a name="Page_207" id="Page_207">[Pg
+207]</a></span>
+
+examined; length of stalk 2&frac12; times length of median ossification
+which is higher than wide, slightly decurved, sagittate in dorsal view,
+with three-cornered base; basal tuberosities of stalk moderately well
+developed, medially joined; posterior profile in dorsal view evenly
+rounded; ventral concavity broader than, but of comparable depth to,
+dorsal concavity in end-view, base of stalk wider ventrally, constriction
+&frac34; greatest depth; at mid-point of stalk shaft is but slightly
+wider than high; pronounced terminal inflation of shaft; lateral profile
+in dorsal view sloping abruptly from widest point of stalk anteriorly
+onto stalk which then tapers more gradually to terminal inflation.</p>
+
+<p>From the baculum of its New World counterpart, namely <i>Microtus
+pennsylvanicus</i>, my specimen of <i>Microtus agrestis</i> and the
+specimen figured by Didier (1954:239) differ in their minute lateral
+processes, relatively larger median processes, and more elongate, less
+dorsoventrally flattened shafts.</p>
+
+<p>The specimen of <i>M. agrestis</i> figured by Ognev (1950:320), in
+dorsal view has lateral concavities producing a somewhat trilobate
+outline in the base of the stalk, and the lateral processes are well
+developed; the median process is larger and bulbous, wider distally than
+proximally. Without larger numbers of bacula of <i>M. agrestis</i> I am
+unable to reconcile these differences. The differences between <i>M.
+agrestis</i> and <i>M. pennsylvanicus</i> seem comparable to the
+differences between some other species of <i>Microtus</i>.</p>
+
+<p><i>Specimen examined</i>: One, from Gryon, Switzerland, 67102.</p>
+
+
+<h3>Microtus (Pedomys) ochrogaster (Wagner)</h3>
+<p class="center">Fig. 31</p>
+
+<p>Baculum: Stalk broad, greatest length (3.2-4.0 mm.)
+1<sup>2</sup>/<sub>3</sub> to 2 times greatest breadth, 2&frac12; to 4
+times greatest depth; median process ossified, relatively small, less
+than <sup>3</sup>/<sub>10</sub> length of stalk; lateral processes
+arising from subterminal part of stalk, cartilaginous or with small
+ossifications; posterior profile in dorsal view broadly rounded or
+slightly angular, widest point of stalk <sup>1</sup>/<sub>6</sub> to
+&frac14; the length of stalk from base; basal tuberosities well developed
+and medially confluent, in end-view dorsally convex, or at least less
+deeply concave than ventrally; shaft straight, base bent ventrally or
+more commonly dorsally; at mid-point of stalk wider than high, often
+twice as wide as high; viewed from above, lateral profile from point of
+greatest breadth to middle of shaft a gradual sigmoid curve; slight
+terminal inflation of shaft.</p>
+
+<p><i>Specimens examined</i>: Forty-one, of three subspecies; <i>Microtus
+ochrogaster haydeni</i>, Muir Springs, 2 mi. N, 2&frac12; mi. W Ft.
+Morgan, Morgan Co., Colorado, 74995, 74998, 74999, 75002; 1 mi. W Laird,
+Yuma Co., Colorado, 57304, 76833; 2 mi. N, 2 mi. W Haigler, Dundy Co.,
+Nebraska, 75016; 2 mi. S Franklin, Franklin Co., Nebraska, 75043, 75044;
+Atwood, Rawlins Co., Kansas, 75020, 75023, 75025, 75027, 75028; 1 mi. N,
+2 mi. E Oberlin, Decatur Co., Kansas, 75030, 75032, 75034, 75035, 75036;
+1&frac12; mi. N, &frac14; mi. E Norton, Norton Co., Kansas, 68327; 1 mi.
+SW Norton, Norton Co., Kansas, 75037; 2 mi. S, 1 mi. W Norton, Norton
+Co., Kansas, 75038; <i>M. ochrogaster ochrogaster</i>, Rydal, Republic
+Co., Kansas, 75047-75053, 75060, 75062, 75063, 75066, 75070, 75071,
+75073; 1 mi. N, 1 mi. W Holton, Jackson Co., Kansas, 75077; 2 mi. W Court
+House, Lawrence, Douglas Co., Kansas, 76832; Univ. Kansas Natural History
+Reservation, Douglas Co., Kansas, 68536; <i>M. ochrogaster taylori</i>,
+Meade County State Park, Kansas, 68539, 68542.</p>
+
+<p><span class="pagenum"><a name="Page_208" id="Page_208">[Pg
+208]</a></span></p>
+
+
+<h3>Microtus (Pitymys) pinetorum (LeConte)</h3>
+<p class="center">Figs. 27 and 28</p>
+
+<p>Baculum: Stalk broad, greatest length (2.5 to 2.7 mm.)
+1<sup>2</sup>/<sub>3</sub> times greatest breadth, 4 times greatest
+depth; median process ossified, size small, <sup>1</sup>/<sub>5</sub>
+length of stalk, higher than wide, having small anterodorsal prominence
+in both specimens examined; lateral processes cartilaginous, relatively
+small, displaced posteriorly, attenuate; posterior margin in dorsal view
+broadly rounded, or having blunt median apex, convex throughout; basal
+tuberosities moderately well developed, medially confluent, barely
+visible in dorsal view when mature; in end-view median constriction
+<sup>4</sup>/<sub>5</sub> greatest depth, ventral concavity deeper than
+dorsal concavity, both comparatively shallow; stalk at mid-point
+1&frac12; times as wide as deep; shaft relatively slender, bowed dorsally
+at tip, relatively straight otherwise; lateral profile in dorsal view a
+gradual concave slope from point of greatest width anteriorly to distal
+part of shaft.</p>
+
+<p><i>Specimens examined</i>: Two, from Douglas Co., Kansas, 76834 (2 mi.
+N Baldwin), 68545 (1 mi. NE Pleasant Grove).</p>
+
+
+<h3>Microtus (Pitymys) parvulus (Howell)</h3>
+<p class="center">Fig. 40</p>
+
+<p>Baculum: Stalk broad, greatest length (2.4 mm. in specimen examined)
+1&frac34; times greatest breadth, 4 times greatest depth; median process
+ossified, size small, less than &frac14; length of stalk, wider than
+high, terminally flattened; lateral processes cartilaginous, relatively
+small, attenuate; posterior margin in dorsal view flattened, irregularly
+curved with concavities medially and laterally; basal tuberosities well
+developed, medially confluent; visible in dorsal view; in end-view median
+constriction <sup>2</sup>/<sub>3</sub> greatest depth, ventral concavity
+well-formed, no dorsal concavity; stalk at mid-point twice as wide as
+deep; shaft relatively slender, bowed dorsally toward tip; in dorsal view
+lateral profile a gradual concave slope from point of greatest width
+anteriorly to distal part of shaft; tip of shaft enlarged.</p>
+
+<p>The baculum of <i>M. parvulus</i> resembles that of <i>M.
+pinetorum</i> more than it resembles the baculum of any other microtine
+studied, differing primarily in smaller size.</p>
+
+<p><i>Specimen examined</i>: One, from 1 mi. W Micanopy, Alachua Co.,
+Florida, Univ. Florida No. 1508.</p>
+
+
+<h3>Microtus (Pitymys) quasiater (Coues)</h3>
+<p class="center">Figs. 29 and 30</p>
+
+<p>Baculum: Stalk broad, greatest length (2.6-3.2 mm.)
+1<sup>1</sup>/<sub>3</sub> to 1<sup>2</sup>/<sub>3</sub> times greatest
+breadth, 3<sup>1</sup>/<sub>3</sub> to 3<sup>2</sup>/<sub>3</sub> times
+greatest depth; median process ossified, with ventral depression, process
+&frac14; to <sup>1</sup>/<sub>3</sub> length of stalk, appressed to tip
+of shaft, wider than high proximally, relatively broad terminally;
+lateral processes cartilaginous, small, attenuate; posterior profile of
+stalk in dorsal view broadly rounded, bilobate, or trilobate, median lobe
+formed by posterior projection of dorsal shelf between enlarged lateral
+tuberosities that form outer lobes, posterolateral faces of these
+tuberosities visible in dorsal view of stalk; in end-view dorsal surface
+slightly concave, ventral concavity broad and deep, median constriction
+
+<span class="pagenum"><a name="Page_209" id="Page_209">[Pg
+209]</a></span>
+
+&frac12; greatest depth; shaft flattened except tip that is more terete,
+and bowed dorsally; at mid-point, stalk twice as wide as high; shaft
+relatively slender terminally, narrower than median ossification.</p>
+
+<p>The baculum of <i>M. quasiater</i> is the largest and has the best
+developed base and median process of the three American species of the
+subgenus <i>Pitymys</i>. The three species closely resemble each other in
+basic form.</p>
+
+<p><i>Specimens examined</i>: Five, all from Veracruz; Teocelo, 4500 ft.,
+30709, 30711; 4 km. N Tlapacoy&aacute;n, 1700 ft., 24466; 5 km. N Jalapa, 4500
+ft., 19869, 19878.</p>
+
+
+<h3>Microtus (Pitymys) fatioi (Mottaz)</h3>
+<p class="center">Fig. 26</p>
+
+<p>The baculum of a single specimen (KU 67103) of <i>M. fatioi</i> from
+Zermatt, Valais, Switzerland, was examined. The baculum is immature, as
+evidenced by its small size, slender stalk and absence of ossified
+processes, therefore no characterization is included.</p>
+
+<p>The baculum of another Old World species of the subgenus
+<i>Pitymys</i>, <i>M. pyrenaicus</i> from France, figured and described
+by Didier (1954:242-243), differs from all New World <i>Pitymys</i>
+examined in processing ossified lateral processes.</p>
+
+<p>The status of <i>Pitymys</i>, as a genus or as a subgenus, is
+uncertain. Hall and Cockrum (1953:448) considered the North American
+<i>Pitymys</i> and <i>Pedomys</i> as subgenera of <i>Microtus</i>. They
+did not state specifically the basis for this point of view, but mention
+the fact that these two subgenera (<i>Pitymys</i> and <i>Pedomys</i>)
+closely resemble each other cranially. These authors did not study nor
+comment upon the status of the Old World <i>Pitymys</i>. It may be asked
+whether the Old World and New World <i>Pitymys</i> have developed as
+fossorial <i>Microtus</i> independently, or from an ancestor common to
+both groups and not common to any other <i>Microtus</i>. Matthey
+(1955:202) found 62 chromosomes (2N) in both the New World <i>Pitymys
+pinetorum</i> and the Old World <i>Pitymys duodecimcostatus</i>. This
+suggests, but does not prove, common ancestry.</p>
+
+
+<h3>Neofiber alleni True</h3>
+<p class="center">Fig. 49</p>
+
+<p>Baculum: Stalk massive, greatest length (4.7 mm.) 1&frac34; times
+greatest breadth, 4 times greatest depth; ossification in digitate
+processes variable; in one (KU 27123) of two specimens examined lateral
+processes ossified and median process unossified, as in two specimens
+examined by Hamilton (1946:379) from "southern Florida"; in my other
+specimen (KU 27268) that is possibly more mature, median process ossified
+although less deeply stained than lateral ossifications or stalk;
+posterior profile in probable dorsal view roughly rounded; in end-view
+probable dorsal concavity deep, ventral concavity broad but shallow, and
+with center convex; median constriction <sup>3</sup>/<sub>5</sub>
+greatest depth; shaft heavy, least depth <sup>2</sup>/<sub>3</sub>
+greatest depth of base; stalk, at mid-point, slightly wider than deep and
+more than <sup>1</sup>/<sub>3</sub> width of base; lateral profile in
+dorsal view sharply incurved distal to point of greatest breadth, shaft
+therefore relatively distinct from basal part of stalk; slight
+subterminal constriction; tip less reduced in the two specimens examined
+than in two figured by Hamilton. In preparation, the tissues that make it
+possible to distinguish
+
+<span class="pagenum"><a name="Page_210" id="Page_210">[Pg
+210]</a></span>
+
+with certainty the dorsal and ventral surfaces of the baculum were
+removed in both specimens.</p>
+
+<p><i>Specimens examined</i>: Two, of the subspecies <i>Neofiber alleni
+alleni</i>, 2 mi. S Gainesville, Alachua Co., Florida, 27268; 1 mi. E
+Courtenay, Merritt Island, Brevard Co., Florida, 27123.</p>
+
+
+<h3>Lagurus curtatus (Cope)</h3>
+<p class="center">Fig. 46</p>
+
+<p>Baculum: Stalk slender, greatest length (2.5 mm.) 2 to
+2<sup>2</sup>/<sub>3</sub> times greatest breadth, 4 to 5 times greatest
+depth; three ossified processes; median one more than
+<sup>1</sup>/<sub>3</sub> length of stalk, curved dorsally toward tip,
+proximally flattened and having acute lateral angles in dorsal view,
+wider than deep except in distal half; lateral processes smaller than
+median one, slenderer, shorter, of approximately same depth, also curved
+dorsally; base of stalk well developed, basal tuberosities medially
+confluent, in part visible in dorsal view, in end-view wider ventrally
+than dorsally, dorsal and ventral concavities of equal depth and both
+wide, medial constriction &frac12; greatest depth; posterior profile in
+dorsal view broadly bilobate; lateral profile with abrupt transition from
+basal tuberosities to gradually converging, slightly curved sides of
+shaft; shaft terminally inflated.</p>
+
+<p>Dearden (1958:543) described and figured the bacula of six subspecies
+of <i>Lagurus curtatus</i> and two Asiatic species, <i>Lagurus
+lagurus</i> and <i>Lagurus luteus</i>. He examined at least 34 specimens
+of <i>L. curtatus</i> and found geographic variation in size, breadth of
+shaft distally, and proportions of digital ossifications to each other
+and to the stalk. The description that I have given above pertains to
+<i>L. c. levidensis</i>.</p>
+
+<p>The baculum of the Asiatic <i>Lagurus (Lagurus) lagurus</i> figured by
+Ognev (1950:554) agrees with that of <i>Lagurus (Lemmiscus) curtatus</i>,
+described here, in the relatively elongate shaft and slender stalk, the
+proportions of the processes, and the well-formed and moderately enlarged
+base of the stalk. The bacula of three <i>Lagurus lagurus</i> examined by
+Dearden (1958:545) were of older individuals than the specimen that Ognev
+figures and differ from it and from bacula of <i>Lagurus curtatus</i>
+(all subspecies) in the unusual, almost heart shaped, median process, and
+in larger size. <i>Lagurus luteus</i> examined by Dearden (1958:545)
+differs from both <i>Lagurus lagurus</i> and <i>Lagurus curtatus</i> in
+lacking lateral digital ossifications and in having shorter median
+digital ossifications and wider base of stalk.</p>
+
+<p><i>Specimens examined</i>: Seven <i>Lagurus curtatus levidensis</i>
+from Wyoming; 9 mi. S Robertson, Uinta Co., 26045, 26053; 8 mi. S,
+2&frac12; mi. E Robertson, Uinta Co., 26049; Farson, Sweetwater Co.,
+37906; 16 mi. S, 11 mi. W Waltman, Natrona Co., 42457; 32 mi. S, 22 mi. E
+Rock Springs, 42465, 42466.</p>
+
+<p style="margin-bottom:2em;">The following key to the bacula in some adult North American
+Microtinae is intended to help point out some of the most important
+differences. It should be noted that not all species can be keyed out on
+the basis of the baculum. The most difficult group in this respect
+includes the species of <i>Microtus</i> that have small or no ossified
+lateral processes, especially species of the subgenera <i>Pedomys</i> and
+<i>Pitymys</i>, and the two species <i>Microtus californicus</i> and
+<i>Microtus mexicanus</i> of the subgenus <i>Microtus</i>. Another
+complicating factor is the variability of bacula evident in some species
+even in the small samples available.
+
+<span class="pagenum"><a name="Page_211" id="Page_211">[Pg
+211]</a></span>
+
+It is to be expected that additional specimens will show variations not
+yet observed.</p>
+
+<h2 class="smcap">Key to the Bacula of Some North American Microtines</h2>
+
+
+<table class="key">
+	<tr>
+		<td class="text">1. Length of lateral digital ossifications more than <sup>1</sup>/<sub>3</sub> breadth of stalk</td>
+		<td class="number">2</td>
+	</tr>
+	<tr>
+		<td class="text">1´. Length of lateral digital ossifications less than <sup>1</sup>/<sub>3</sub> breadth of stalk or absent</td>
+		<td class="number">15</td>
+	</tr>
+	<tr>
+		<td class="text">2. Size small (total length of baculum less than 5.5 mm.)</td>
+		<td class="number">3</td>
+	</tr>
+	<tr>
+		<td class="text">2´. Size large (total length of baculum more than 5.5 mm.)</td>
+		<td class="number">14</td>
+	</tr>
+	<tr>
+		<td class="text">3. Width at mid-point of stalk more than <sup>1</sup>/<sub>3</sub> greatest breadth of stalk</td>
+		<td class="number">4</td>
+	</tr>
+	<tr>
+		<td class="text">2´. Size large (total length of baculum more than 5.5 mm.)</td>
+		<td class="number">14</td>
+	</tr>
+	<tr>
+		<td class="text">3´. Width at mid-point of stalk less than <sup>1</sup>/<sub>3</sub> greatest breadth of stalk,</td>
+		<td class="number">8</td>
+	</tr>
+	<tr>
+		<td class="text">4. Stalk, viewed from proximal end hour-glass shaped, and width
+		  of stalk less than &frac12; length of stalk.... <i>Phenacomys
+		  intermedius</i>,</td>
+		<td class="number"><a href="#Page_197">p. 197</a></td>
+	</tr>
+	<tr>
+		<td class="text">4´. Stalk not both hour-glass shaped when viewed from proximal
+		  end, and with width less than &frac12; length of stalk</td>
+		<td class="number">5</td>
+	</tr>
+	<tr>
+		<td class="text">5. Shaft thin basally, thickness less than <sup>1</sup>/<sub>3</sub> of greatest breadth</td>
+		<td class="number">6</td>
+	</tr>
+	<tr>
+		<td class="text">5´. Shaft thick basally, thickness <sup>1</sup>/<sub>3</sub> or more of greatest breadth</td>
+		<td class="number">7</td>
+	</tr>
+	<tr>
+		<td class="text">6. Stalk more or less straight, base not deflected. <i>Microtus
+		  oeconomus</i>,</td>
+		<td class="number"><a href="#Page_204">p. 204</a></td>
+	</tr>
+	<tr>
+		<td class="text">6´. Stalk spatulate, and base deflected from axis of shaft....
+		  <i>Microtus guatemalensis</i>,</td>
+		<td class="number"><a href="#Page_198">p. 198</a></td>
+	</tr>
+	<tr>
+		<td class="text">7. Base enlarged, depth nearly &frac12; of breadth.... <i>Lemmus
+		  trimucronatus</i>,</td>
+		<td class="number"><a href="#Page_193">p. 193</a></td>
+	</tr>
+	<tr>
+		<td class="text">7´. Base moderately enlarged, depth near <sup>1</sup>/<sub>3</sub> of breadth....
+		  <i>Microtus pennsylvanicus</i>, <a href="#Page_206">p. 206</a>, or <i>Microtus townsendii</i>,</td>
+		<td class="number"><a href="#Page_204">p. 204</a></td>
+	</tr>
+	<tr>
+		<td class="text">8. Base hour-glass shaped as viewed from proximal end....
+		  <i>Phenacomys intermedius</i>,</td>
+		<td class="number"><a href="#Page_197">p. 197</a></td>
+	</tr>
+	<tr>
+		<td class="text">8´. Not so</td>
+		<td class="number">9</td>
+	</tr>
+	<tr>
+		<td class="text">9. Lateral processes separated from tip of shaft by more than the
+		  thickness of the lateral process</td>
+		<td class="number">10</td>
+	</tr>
+	<tr>
+		<td class="text">9´. Lateral processes separated from tip of shaft by less than the
+		  thickness of the lateral process</td>
+		<td class="number">11</td>
+	</tr>
+	<tr>
+		<td class="text">10. Lateral processes more than &frac12; the width of median
+		  process.... <i>Microtus longicaudus</i>,</td>
+		<td class="number"><a href="#Page_201">p. 201</a></td>
+	</tr>
+	<tr>
+		<td class="text">10´. Lateral processes slender, less than &frac12; the width of median
+		  process.... <i>Microtus montanus</i>,</td>
+		<td class="number"><a href="#Page_204">p. 204</a></td>
+	</tr>
+	<tr>
+		<td class="text">11. Lateral ossifications equal in length to median
+		  ossification.... <i>Clethrionomys</i>,</td>
+		<td class="number"><a href="#Page_194">p. 194</a></td>
+	</tr>
+	<tr>
+		<td class="text">11´. Lateral ossifications shorter than median ossification</td>
+		<td class="number">12</td>
+	</tr>
+	<tr>
+		<td class="text">12. Size small, less than 3.4 mm. in total length....
+		  <i>Microtus oregoni</i>,</td>
+		<td class="number"><a href="#Page_199">p. 199</a></td>
+	</tr>
+	<tr>
+		<td class="text">12´. Size medium, more than 3.4 mm. in total length</td>
+		<td class="number">13</td>
+	</tr>
+	<tr>
+		<td class="text">13. Greatest width of stalk at a point about <sup>1</sup>/<sub>3</sub> of length of
+		  stalk from base.... <i>Microtus chrotorrhinus</i> (Hamilton, 1946:382).</td>
+		<td class="number">&nbsp;</td>
+	</tr>
+	<tr>
+		<td class="text">13´. Greatest width of stalk at a point less than <sup>1</sup>/<sub>3</sub> of length of
+		  stalk from base.... <i>Lagurus curtatus</i>,</td>
+		<td class="number"><a href="#Page_210">p. 210</a></td>
+	</tr>
+	<tr>
+		<td class="text">14. Size of baculum larger, base more than 3 mm. wide, processes
+		  all well developed.... <i>Ondatra zibethicus</i>,</td>
+		<td class="number"><a href="#Page_198">p. 198</a></td>
+	</tr>
+	<tr>
+		<td class="text">14´. Size of baculum smaller, base less than 3 mm. wide, processes
+		  poorly developed in some animals.... <i>Neofiber alleni</i>,</td>
+		<td class="number"><a href="#Page_209">p. 209</a></td>
+	</tr>
+	<tr>
+		<td class="text">15. At least one digital ossification present</td>
+		<td class="number">16</td>
+	</tr>
+	<tr>
+		<td class="text">
+			<span class="pagenum"><a name="Page_212" id="Page_212">[Pg
+			212]</a></span>
+			15´. Digital ossifications not present.... <i>Dicrostonyx groenlandicus</i>,</td>
+		<td class="number"><a href="#Page_193">p. 193</a></td>
+	</tr>
+	<tr>
+		<td class="text">16. Breadth of stalk at least &frac12; length of stalk</td>
+		<td class="number">17</td>
+	</tr>
+	<tr>
+		<td class="text">16´. Breadth of stalk less than &frac12; length of stalk</td>
+		<td class="number">19</td>
+	</tr>
+	<tr>
+		<td class="text">17. Length of stalk greater than 3.6 mm. and less than 1&frac12;
+		  times its greatest breadth.... <i>Microtus richardsoni</i>,</td>
+		<td class="number"><a href="#Page_199">p. 199</a></td>
+	</tr>
+	<tr>
+		<td class="text">17´. Length of stalk usually less than 3.6 mm., or if more than
+		  3.6 mm. (up to 4.0 mm.) then length 1&frac12; times or more its
+		  greatest breadth</td>
+		<td class="number">18</td>
+	</tr>
+	<tr>
+		<td class="text">18. Median process attenuate distally in dorsal view, and
+		  relatively long (more than twice its own breadth), <sup>1</sup>/<sub>5</sub> to <sup>3</sup>/<sub>5</sub> the
+		  length of stalk; breadth of stalk usually <sup>2</sup>/<sub>3</sub> or more length of
+		  stalk.... <i>Microtus miurus</i>,</td>
+		<td class="number"><a href="#Page_200">p. 200</a></td>
+	</tr>
+	<tr>
+		<td class="text">18´. Median process relatively blunt distally in dorsal view,
+		  relatively short (usually less than &frac14; length of stalk), breadth
+		  of stalk usually less than <sup>2</sup>/<sub>3</sub> length of stalk....
+		  <i>Pitymys</i>, <a href="#Page_208">p. 208</a>, <i>Pedomys</i>, <a href="#Page_207">p. 207</a>, or <i>Microtus mexicanus</i>,</td>
+		<td class="number"><a href="#Page_205">p. 205</a></td>
+	</tr>
+	<tr>
+		<td class="text">19. Distal processes small and firmly ankylosed to distal end of
+		  shaft.... <i>Phenacomys longicaudus</i>,</td>
+		<td class="number"><a href="#Page_197">p. 197</a></td>
+	</tr>
+	<tr>
+		<td class="text">19´. Distal processes if present not firmly ankylosed to distal
+		  end of shaft</td>
+		<td class="number">20</td>
+	</tr>
+	<tr>
+		<td class="text">20. Dorsal concavity of base as viewed from proximal end usually
+		  deeper than ventral concavity.... <i>Microtus mexicanus</i>,</td>
+		<td class="number"><a href="#Page_205">p. 205</a></td>
+	</tr>
+	<tr>
+		<td class="text">20´. Dorsal and ventral concavities of base equal in depth or
+		  ventral one the deeper</td>
+		<td class="number">21</td>
+	</tr>
+	<tr>
+		<td class="text">21. Total length of baculum more than 3.6 mm.... <i>Microtus
+		  californicus</i>,</td>
+		<td class="number"><a href="#Page_205">p. 205</a></td>
+	</tr>
+	<tr>
+		<td class="text">21´. Total length of baculum less than 3.6 mm.... <i>Synaptomys
+		  cooperi</i>,</td>
+		<td class="number"><a href="#Page_194">p. 194</a></td>
+	</tr>
+</table>
+
+
+<h2>DISCUSSION</h2>
+
+<p>Owing to shortness of lower incisors and present geographic
+distribution of the species, Hinton (1926:35) considered the Tribe Lemmi
+(lemmings) to be more primitive than the Tribe Microti (voles). The
+surviving lemmings are specialized in many features and therefore are
+considered as advanced end-products of an evolutionary radiation of a
+primitive microtine stock, of which all earlier stages are extinct.</p>
+
+<p>Hinton regarded <i>Dicrostonyx</i> as the most primitive of the genera
+of lemmings on account of its more complex molar teeth (complexity was
+considered to be primitive), and on account of the presence of three
+primitive longitudinal rows of tubercles in unworn molars. The other
+three genera were arranged in order of increasing specialization as
+follows: <i>Synaptomys</i>, <i>Myopus</i>, <i>Lemmus</i>.</p>
+
+<p>If the baculum tended to retain its primitive character while
+specializations in the external anatomy developed, and if the above
+arrangement is correct the most primitive bacula would be found
+in <i>Dicrostonyx</i> and in <i>Synaptomys</i>. The baculum in these two
+genera in comparison to that in <i>Myopus</i> (as figured by Ognev, 1948:512)
+
+<span class="pagenum"><a name="Page_213" id="Page_213">[Pg 213]</a></span>
+
+and <i>Lemmus</i> has a slenderer stalk and smaller digital ossifications
+or none at all. The baculum in the genera of lemmings increases in
+robustness and the development of processes from <i>Dicrostonyx</i>, to
+<i>Synaptomys</i>, to <i>Myopus</i>, to <i>Lemmus</i>&mdash;the same
+order outlined above for total of specialization. The two extremes in
+this series are near the extremes of variation in bacula to be found in
+all microtines. The baculum in lemmings as a group cannot then be
+considered more primitive than in voles as a group, although the voles
+are usually considered to be more advanced. The situation in the voles,
+as we shall see, casts a different light on the matter.</p>
+
+<p>The voles, Tribe Microti, were considered by Hinton (1926:40) to be
+more advanced than the lemmings because the incisors of the voles are
+longer and the root of their last lower molar is lingual to the root of
+the incisor. Hinton thought also that the murine ancestors of microtines
+had shorter incisors and that the backward extension of the incisors in
+the voles is a more ancient feature than the hypsodonty of the molars. A
+trend in the molar teeth has been toward greater hypsodonty. The voles in
+which the molars are least hypsodont are thus considered primitive. These
+include the living genera <i>Clethrionomys</i>, <i>Phenacomys</i>,
+<i>Ondatra</i>, <i>Dolomys</i>, <i>Ellobius</i>, and <i>Prometheomys</i>.
+Therefore, the baculum, in these assumedly primitive genera, would be
+expected to resemble the baculum in the lemmings or at least the most
+primitive lemmings. This is not the case.</p>
+
+<p>The bacula that I have examined of <i>Clethrionomys</i> and
+<i>Phenacomys</i> have well-developed digital ossifications. In this they
+resemble the baculum of the genus <i>Lemmus</i>, the most advanced genus
+of lemmings according to Hinton. The baculum of <i>Dolomys</i> has not
+been studied. The baculum in <i>Ondatra</i>, and in <i>Prometheomys</i>
+as illustrated by Ognev (1948:552), also possesses well-developed
+processes. The baculum of <i>Ellobius</i> is small and lacks processes
+(as figured by Ognev, 1950:662). No ossification was found in a single
+specimen of <i>Ellobius</i> examined by me although the entire glans
+penis was removed and cleared without dissection. So far as known then,
+with the exception of <i>Ellobius</i> and <i>Phenacomys longicaudus</i>
+(Dearden, 1958:547), the primitive microtines having rooted molars
+possess bacula having three well-developed ossified processes.</p>
+
+<p>Voles of the genus <i>Microtus</i> vary in the structure of the
+baculum almost as much as do the lemmings. Within the single subgenus
+<i>Microtus</i> some individuals of <i>Microtus mexicanus</i>, for
+example, have minute ossified lateral processes and other individuals
+lack these
+
+<span class="pagenum"><a name="Page_214" id="Page_214">[Pg 214]</a></span>
+
+processes; <i>Microtus pennsylvanicus</i> and some other species have
+proportionately large lateral ossifications. If the well-developed
+condition of the baculum in the microtines having rooted molars is
+primitive, then within the genus <i>Microtus</i> those species having
+well-developed bacula may be considered primitive.</p>
+
+<p>The genera <i>Lagurus</i> and <i>Neofiber</i> have moderately
+developed or well-developed lateral processes. <i>Neofiber</i> exhibits a
+tendency, not prominent elsewhere, to have a proportionately smaller
+median process rather than reduced lateral processes.</p>
+
+<p>American species of <i>Microtus</i> (genus and subgenus) that have
+moderately- to well-developed ossified lateral processes are <i>M.
+townsendii</i>, <i>M. oeconomus</i>, <i>M. pennsylvanicus</i>, <i>M.
+montanus</i>, and <i>M. chrotorrhinus</i>. <i>Microtus</i> of other
+subgenera having this type of baculum include <i>M. (Herpetomys)
+guatemalensis</i>, <i>M. (Chilotus) oregoni</i>, and <i>M. (Chionomys)
+longicaudus</i>.</p>
+
+<p>American species of <i>Microtus</i> (genus and subgenus) in which the
+lateral ossifications are weakly developed or absent (although
+cartilaginous lateral processes are present) include <i>M. mexicanus</i>
+and <i>M. californicus</i>. In other subgenera, species of
+<i>Microtus</i> having reduced lateral ossifications are <i>M. (Pedomys)
+ochrogaster</i>, <i>M. (Pitymys) pinetorum</i>, <i>M. (Pitymys)
+parvulus</i>, <i>M. (Pitymys) quasiater</i>, <i>M. (Arvicola)
+richardsoni</i>, and <i>M. (Stenocranius) miurus</i>.</p>
+
+<p>The microtines are essentially holarctic in distribution. Both of the
+tribes, the lemmings and the voles, as well as primitive representatives
+of each tribe (not considering <i>Ellobius</i>) occur in both the Old
+World and New World. It is not certain on which continent (or continents)
+the Microtinae first differentiated. It is certain, however, that at
+various times, both early and late in the evolution of the subfamily,
+representatives have crossed from Eurasia to North America or <i>vice
+versa</i>. Each of 10 or more microtines in the New World is more closely
+related to some microtine in the Old World than to any other microtine in
+the New World.</p>
+
+<p>The similarities or differences in the baculum in Old World and New
+World representatives placed in the same genus or subgenus, or thought to
+be "companion species" have been commented upon in accounts of
+<i>Lemmus</i>, <i>Dicrostonyx</i>, <i>Clethrionomys</i>, <i>Lagurus</i>,
+<i>Arvicola</i>, <i>Stenocranius</i>, <i>Chilotus</i>, <i>Chionomys</i>,
+<i>Pitymys</i>, and in accounts of <i>Microtus agrestis</i> as compared
+with <i>M. pennsylvanicus</i>, and <i>Microtus oeconomus</i> (both Old
+World and New World).</p>
+
+<p>The baculum in the Microtinae more closely resembles the baculum in
+the Cricetinae of the Old World than in the Murinae, or than in any other
+rodents known to me. This resemblance suggests relationship between
+Microtinae and Cricetinae.</p>
+
+
+<p><span class="pagenum"><a name="Page_215" id="Page_215">[Pg 215]</a></span></p>
+
+<h2>LITERATURE CITED</h2>
+
+<table>
+	<tr>
+		<td colspan="2" class="smcap">Argyropulo, A. I.</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1933a.</td>
+		<td class="litcit_txt">Die Gattungen und Arten der Hamster (<i>Cricetinae</i> Murray, 1866) der Pal&auml;arktik. Zeitschr. f.
+S&auml;ugetierkunde, 8:129-149, 27 figs. in text.</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1933b.</td>
+		<td class="litcit_txt">&uuml;ber zwei neue pal&auml;arktische W&uuml;hlm&auml;use. Zeitschr. f. S&auml;ugetierkunde, 8:180-183, 3 figs. in text.</td>
+	</tr>
+	<tr>
+		<td colspan="2" class="smcap">Callery, R.</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1951.</td>
+		<td class="litcit_txt">Development of the os genitale in the golden hamster, <i>Mesocricetus (Cricetus) auratus</i>. Jour. Mamm.,
+32:204-207, 1 fig. in text.</td>
+	</tr>
+	<tr>
+		<td colspan="2" class="smcap">Chamberlain, J. L.</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1954.</td>
+		<td class="litcit_txt">The Block Island meadow mouse, <i>Microtus provectus</i>. Jour. Mamm., 35:587-589, 2 tables in text.</td>
+	</tr>
+	<tr>
+		<td colspan="2" class="smcap">Dearden, L. C.</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1958.</td>
+		<td class="litcit_txt">The baculum in <i>Lagurus</i> and related microtines. Jour. Mamm., 39:541-553, 1 fig. in text.</td>
+	</tr>
+	<tr>
+		<td colspan="2" class="smcap">Didier, R.</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1943.</td>
+		<td class="litcit_txt">L'os p&eacute;nien des Campagnols de France du Genre <i>Arvicola</i>. Mammalia, 7:74-79, 10 figs. in text.</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1954.</td>
+		<td class="litcit_txt">Etude syst&eacute;matique de l'os p&eacute;nien des Mammif&egrave;res (suite), Rongeurs: Murid&eacute;s. Mammalia, 18:237-256, 14 figs. in
+text.</td>
+	</tr>
+	<tr>
+		<td colspan="2" class="smcap">Ellerman, J. R.</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1941.</td>
+		<td class="litcit_txt">The families and genera of living rodents. Vol. II. Family Muridae. The British Museum (Natural History), London,
+pp. xii + 690, 50 figs.</td>
+	</tr>
+	<tr>
+		<td colspan="2" class="smcap">Friley, Charles E.</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1947.</td>
+		<td class="litcit_txt">Preparation and preservation of the baculum of mammals. Jour. Mamm., 28:395-397, 1 fig. in text.</td>
+	</tr>
+	<tr>
+		<td colspan="2"><span class="smcap">Hall, E. R.</span>, and <span class="smcap">E. L. Cockrum.</span></td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1953.</td>
+		<td class="litcit_txt">A synopsis of the North American microtine rodents. Univ. Kansas Publ., Mus. Nat. Hist., 5:373-498, 149 figs. in
+text.</td>
+	</tr>
+	<tr>
+		<td colspan="2" class="smcap">Hamilton, W. J., Jr.</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1946.</td>
+		<td class="litcit_txt">A study of the baculum in some North American Microtinae. Jour. Mamm., 27:378-387, 3 figs. in text.</td>
+	</tr>
+	<tr>
+		<td colspan="2"><span class="smcap">Hibbard, C. W.</span>, and <span class="smcap">G. C. Rinker.</span></td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1942.</td>
+		<td class="litcit_txt">A new bog-lemming (Synaptomys) from Meade County, Kansas. Univ. Kansas Sci. Bull., 28:25-35, 3 figs. in text.</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1943.</td>
+		<td class="litcit_txt">A new meadow mouse (<i>Microtus ochrogaster taylori</i>) from Meade County, Kansas. Univ. Kansas Sci.
+Bull., 29:255-268, 5 figs. in text.</td>
+	</tr>
+	<tr>
+		<td colspan="2" class="smcap">Hinton, M. A. C.</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1926.</td>
+		<td class="litcit_txt">Monograph of the voles and lemmings (Microtinae), living and extinct, Vol. I. British Museum (Natural
+History), London, pp. xvi + 488, plus 15 plates, 110 figs. in text.</td>
+	</tr>
+	<tr>
+		<td colspan="2" class="smcap">Matthey, R.</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1953.</td>
+		<td class="litcit_txt">Les Chromosomes des Muridae. Revue Suisse de Zoologie, 60:225-283, avec les planches 1 &agrave; 4 groupant 84
+photomicrographies, 98 figures et 5 schemas dans le texte.</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1955.
+			<span class="pagenum"><a name="Page_216" id="Page_216">[Pg 216]</a></span></td>
+		<td class="litcit_txt">	Nouveaux documents sur les chromosomes des Muridae. Probl&egrave;mes de cytologie compar&eacute;e et de taxonomie chez les
+Microtinae. Revue Suisse de Zoologie, 62:163-206, avec 114 figures.</td>
+	</tr>
+	<tr>
+		<td colspan="2" class="smcap">Miller, G. S.</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1896.</td>
+		<td class="litcit_txt">Genera and subgenera of voles and lemmings. North American Fauna No. 12, pp. 1-85, 40 figs. and 3 plates in
+text.</td>
+	</tr>
+	<tr>
+		<td colspan="2" class="smcap">Ognev, S. I.</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1948.</td>
+		<td class="litcit_txt">The mammals of Russia (USSR) and adjacent countries (The mammals of Eastern Europe and Northern Asia), Vol. 6.
+Publ. Acad. Sci. USSR, pp. 1-587, 260 figs., 12 maps, and 11 color plates
+in text (in Russian).</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1950.</td>
+		<td class="litcit_txt">The mammals of Russia (USSR) and adjacent countries (The mammals of Eastern Europe and Northern Asia), Vol. 7.
+Publ. Acad. Sci. USSR, pp. 1-736, 347 figs., 15 maps, and 10 color plates
+in text (in Russian).</td>
+	</tr>
+	<tr>
+		<td colspan="2" class="smcap">Ruth, E. B.</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1934.</td>
+		<td class="litcit_txt">The os priapi: A study in bone development. Anat. Rec., 60:231-249, 16 figs. in 3 plates.</td>
+	</tr>
+	<tr>
+		<td colspan="2"><span class="smcap">Smith, D. A.</span>, and <span class="smcap">J. B. Foster.</span></td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1957.</td>
+		<td class="litcit_txt">Notes on the small mammals of Churchill, Manitoba. Jour. Mamm., 38:98-115, 3 figs. and 3 tables in text.</td>
+	</tr>
+	<tr>
+		<td colspan="2" class="smcap">Wheeler, B.</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1956.</td>
+		<td class="litcit_txt">Comparison of the Block Island "species" of <i>Microtus</i> with <i>M. pennsylvanicus</i>. Evolution, 10:176-186,
+4 figs. and 2 tables in text.</td>
+	</tr>
+	<tr>
+		<td colspan="2" class="smcap">White, J. A.</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1951.</td>
+		<td class="litcit_txt">A practical method for mounting the bacula of small mammals. Jour. Mamm., 32:125.</td>
+	</tr>
+	<tr>
+		<td colspan="2" class="smcap">Zimmerman, K.</td>
+	</tr>
+	<tr>
+		<td class="litcit_num">1955.</td>
+		<td class="litcit_txt">Die Gattung <i>Arvicola</i> Lac. im System der Microtinae. S&auml;ugetierkundliche Mitteilungen, 3:110-112, 2 figs. in
+text.</td>
+	</tr>
+	<tr>
+		<td colspan="2"><i>Transmitted August 14, 1959.</i></td>
+	</tr>
+</table>
+
+<p class="center">28-774</p>
+
+<hr />
+
+
+<p><span class="pagenum"><a name="front_flap" id="front_flap">[Front Cover Inside]</a></span></p>
+
+<h2>UNIVERSITY OF KANSAS PUBLICATIONS<br />
+MUSEUM OF NATURAL HISTORY</h2>
+
+<p>Institutional libraries interested in publications exchange may obtain
+this series by addressing the Exchange Librarian, University of Kansas
+Library, Lawrence, Kansas. Copies for individuals, persons working in a
+particular field of study, may be obtained by addressing instead the
+Museum of Natural History, University of Kansas, Lawrence, Kansas. There
+is no provision for sale of this series by the University Library which
+meets institutional requests, or by the Museum of Natural History which
+meets the requests of individuals. However, when individuals request
+copies from the Museum, 25 cents should be included, for each separate
+number that is 100 pages or more in length, for the purpose of defraying
+the costs of wrapping and mailing.</p>
+
+<p>* An asterisk designates those numbers of which the Museum's supply
+(not the Library's supply) is exhausted. Numbers published to date, in
+this series, are as follows:</p>
+
+	<dl>
+		<dt>Vol. 1.</dt>
+			<dd>Nos. 1-26 and index. Pp. 1-638, 1946-1950.</dd>
+
+		<dt>*Vol. 2.</dt>
+			<dd>(Complete) Mammals of Washington. By Walter W. Dalquest. Pp. 1-444, 140 figures in text. April 9, 1948.</dd>
+
+		<dt>Vol. 3.</dt>
+			<dd class="small_margin"><ol class="start_1">
+				<li>*The avifauna of Micronesia, its origin, evolution, and distribution. By Rollin
+				H. Baker. Pp. 1-359, 16 figures in text. June 12, 1951.</li>
+				<li>*A quantitative study of the nocturnal migration of birds. By George H.
+				Lowery, Jr. Pp. 361-472, 47 figures in text. June 29, 1951.</li>
+				<li>Phylogeny of the waxwings and allied birds. By M. Dale Arvey. Pp. 473-530,
+				49 figures in text, 13 tables. October 10, 1951.</li>
+				<li>Birds from the state of Veracruz, Mexico. By George H. Lowery, Jr., and
+				Walter W. Dalquest. Pp. 531-649, 7 figures in text, 2 tables. October 10,
+				1951.</li>
+			</ol></dd>
+			<dd>Index. Pp. 651-681.</dd>
+		<dt>*Vol. 4.</dt>
+			<dd>(Complete) American weasels. By E. Raymond Hall. Pp. 1-466, 41 plates, 31
+			figures in text. December 27, 1951.</dd>
+		<dt>Vol. 5.</dt>
+			<dd>Nos. 1-37 and index. Pp. 1-676, 1951-1953.</dd>
+		<dt>*Vol. 6.</dt>
+			<dd>(Complete) Mammals of Utah, <i>taxonomy</i> and <i>distribution</i>. By Stephen D.
+			Durrant. Pp. 1-549, 91 figures in text, 30 tables. August 10, 1952.</dd>
+		<dt>Vol. 7.</dt>
+		<dd class="small_margin">
+			<ol class="start_1">
+				<li>*Mammals of Kansas. By E. Lendell Cockrum. Pp. 1-303, 73 figures in text,
+				37 tables. August 25, 1952.</li>
+
+				<li>Ecology of the opossum on a natural area in northeastern Kansas. By Henry
+				S. Fitch and Lewis L. Sandidge. Pp. 305-338, 5 figures in text. August
+				24, 1953.</li>
+				<li>The silky pocket mice (Perognathus flavus) of Mexico. By Rollin H. Baker.
+				Pp. 339-347, 1 figure in text. February 15, 1954.</li>
+				<li>North American jumping mice (Genus Zapus). By Phillip H. Krutzsch. Pp.
+				349-472, 47 figures in text, 4 tables. April 21, 1954.</li>
+				<li>Mammals from Southeastern Alaska. By Rollin H. Baker and James S.
+				Findley. Pp. 473-477. April 21, 1954.</li>
+				<li>Distribution of Some Nebraskan Mammals. By J. Knox Jones, Jr. Pp. 479-487.
+				April 21, 1954.</li>
+				<li>Subspeciation in the montane meadow mouse, Microtus montanus, in Wyoming
+				and Colorado. By Sydney Anderson. Pp. 489-506, 2 figures in text.
+				July 23, 1954.</li>
+				<li>A new subspecies of bat (Myotis velifer) from southeastern California and
+				Arizona. By Terry A. Vaughan. Pp. 507-512. July 23, 1954.</li>
+				<li>Mammals of the San Gabriel mountains of California. By Terry A. Vaughan.
+				Pp. 513-582, 1 figure in text, 12 tables. November 15, 1954.</li>
+				<li>A new bat (Genus Pipistrellus) from northeastern Mexico. By Rollin H.
+				Baker. Pp. 583-586. November 15, 1954.</li>
+				<li>A new subspecies of pocket mouse from Kansas. By E. Raymond Hall. Pp.
+				587-590. November 15, 1954.</li>
+				<li>Geographic variation in the pocket gopher, Cratogeomys castanops, in Coahuila,
+				Mexico. By Robert J. Russell and Rollin H. Baker. Pp. 591-608.
+				March 15, 1955.</li>
+				<li>A new cottontail (Sylvilagus floridanus) from northeastern Mexico. By Rollin
+				H. Baker. Pp. 609-612. April 8, 1955.</li>
+				<li>Taxonomy and distribution of some American shrews. By James S. Findley.
+				Pp. 613-618. June 10, 1955.</li>
+				<li>The pigmy woodrat, Neotoma goldmani, its distribution and systematic position.
+				By Dennis G. Rainey and Rollin H. Baker. Pp. 619-624, 2 figures in
+				text. June 10, 1955.</li>
+			</ol></dd>
+			<dd>Index. Pp. 625-651.</dd>
+		<dt><span class="pagenum"><a name="back_flap" id="back_flap">[Back Cover Inside]</a></span>
+			Vol. 8.</dt>
+		<dd class="small_margin">
+			<ol class="start_1">
+				<li>Life history and ecology of the five-lined skink, Eumeces fasciatus.
+By Henry S. Fitch. Pp. 1-156, 26 figures in text. September 1, 1954.</li>
+<li>Myology and serology of the Avian Family Fringillidae, a taxonomic
+study. By William B. Stallcup. Pp. 157-211, 23 figures in text, 4 tables.
+November 15, 1954.</li>
+
+ <li>An ecological study of the collared lizard (Crotaphytus collaris).
+By Henry S. Fitch. Pp. 213-274, 10 figures in text. February 10,
+1956.</li>
+
+ <li>A field study of the Kansas ant-eating frog, Gastrophryne olivacea.
+By Henry S. Fitch. Pp. 275-306, 9 figures in text. February 10,
+1956.</li>
+
+ <li>Check-list of the birds of Kansas. By Harrison B. Tordoff. Pp.
+307-359, 1 figure in text. March 10, 1956.</li>
+
+ <li>A population study of the prairie vole (Microtus ochrogaster) in
+northeastern Kansas. By Edwin P. Martin. Pp. 361-416, 19 figures in text.
+April 2, 1956.</li>
+
+ <li>Temperature responses in free-living amphibians and reptiles of
+northeastern Kansas. By Henry S. Fitch. Pp. 417-476, 10 figures in text,
+6 tables. June 1, 1956.</li>
+
+ <li>Food of the crow, Corvus brachyrhynchos Brehm, in south-central
+Kansas. By Dwight Platt. Pp. 477-498, 4 tables. June 8, 1956.</li>
+
+ <li>Ecological observations on the woodrat Neotoma floridana. By Henry
+S. Fitch and Dennis G. Rainey. Pp. 499-533, 3 figures in text. June 12,
+1956.</li>
+
+ <li>Eastern woodrat, Neotoma floridana; Life history and ecology. By
+Dennis G. Rainey. Pp. 535-646, 12 plates, 13 figures in text. August 15,
+1956.</li>
+			</ol></dd>
+			<dd>Index. Pp. 647-675.</dd>
+		<dt>Vol. 9.</dt>
+			<dd class="small_margin">
+			<ol class="start_1">
+				<li>Speciation of the wandering shrew. By James S. Findley. Pp. 1-68, 18
+figures in text. December 10, 1955.</li>
+
+ <li>Additional records and extension of ranges of mammals from Utah. By
+Stephen D. Durrant, M. Raymond Lee, and Richard M. Hansen. Pp. 69-80.
+December 10, 1955.</li>
+
+ <li>A new long-eared myotis (Myotis evotis) from northeastern Mexico. By
+Rollin H. Baker and Howard J. Stains. Pp. 81-84. December 10, 1955.</li>
+
+ <li>Subspeciation in the meadow mouse, Microtus pennsylvanicus, in
+Wyoming. By Sydney Anderson. Pp. 85-104, 2 figures in text. May 10,
+1956.</li>
+
+ <li>The condylarth genus Ellipsodon. By Robert W. Wilson. Pp. 105-116, 6
+figures in text. May 19, 1956.</li>
+
+ <li>Additional remains of the multituberculate genus Eucosmodon. By
+Robert W. Wilson. Pp. 117-123, 10 figures in text. May 19, 1956.</li>
+
+ <li>Mammals of Coahuila, Mexico. By Rollin H. Baker. Pp. 125-335, 75
+figures in text. June 15, 1956.</li>
+
+ <li>Comments on the taxonomic status of Apodemus peninsulae, with
+description of a new subspecies from North China. By J. Knox Jones, Jr.
+Pp. 337-346, 1 figure in text, 1 table. August 15, 1956.</li>
+
+ <li>Extensions of known ranges of Mexican bats. By Sydney Anderson. Pp.
+347-351. August 15, 1956.</li>
+
+ <li>A new bat (Genus Leptonycteris) from Coahuila. By Howard J. Stains.
+Pp. 353-356. January 21, 1957.</li>
+
+ <li>A new species of pocket gopher (Genus Pappogeomys) from Jalisco,
+Mexico. By Robert J. Russell. Pp. 357-361. January 21, 1957.</li>
+
+ <li>Geographic variation in the pocket gopher, Thomomys bottae, in
+Colorado. By Phillip M. Youngman. Pp. 363-387, 7 figures in text.
+February 21, 1958.</li>
+
+ <li>New bog lemming (genus Synaptomys) from Nebraska. By J. Knox Jones,
+Jr. Pp. 385-388. May 12, 1958.</li>
+
+ <li>Pleistocene bats from San Josecito Cave, Nuevo León, M&eacute;xico. By J.
+Knox Jones, Jr. Pp. 389-396. December 19, 1958.</li>
+
+ <li>New subspecies of the rodent Baiomys from Central America. By Robert
+L. Packard. Pp. 397-404. December 19, 1958.</li>
+
+ <li>Mammals of the Grand Mesa, Colorado. By Sydney Anderson. Pp.
+405-414, 1 figure in text, May 20, 1959.</li>
+
+ <li>Distribution, variation, and relationships of the montane vole,
+Microtus montanus. By Sydney Anderson. Pp. 415-511, 12 figures in text, 2
+tables. August 1, 1959.</li>
+
+ <li>Conspecificity of two pocket mice, Perognathus goldmani and P.
+artus. By E. Raymond Hall and Marilyn Bailey Ogilvie. Pp. 513-518, 1 map
+in text. January 14, 1960.</li>
+
+ <li>Records of harvest mice, Reithrodontomys, from Central America, with
+description of a new subspecies from Nicaragua. By Sydney Anderson and J.
+Knox Jones, Jr. Pp. 519-529. January 14, 1960.</li>
+
+ <li>Small carnivores from San Josecito Cave (Pleistocene), Nuevo León,
+M&eacute;xico. By E. Raymond Hall. Pp. 531-538, 1 figure in text. January 14,
+1960.</li>
+
+ <li>Pleistocene pocket gophers from San Josecito Cave, Nuevo León,
+M&eacute;xico. By Robert J. Russell. Pp. 539-548, 1 figure in text, January 14,
+1960.</li>
+		</ol></dd>
+			<dd>More numbers will appear in volume 9.</dd>
+		<dt><span class="pagenum"><a name="back_flap_out" id="back_flap_out">[Back Cover Outside]</a></span>
+			Vol. 10.</dt>
+			<dd class="small_margin">
+			<ol class="start_1">
+				<li>Studies of birds killed in nocturnal migration. By Harrison B.
+Tordoff and Robert M. Mengel. Pp. 1-44, 6 figures in text, 2 tables.
+September 12, 1956.</li>
+
+ <li>Comparative breeding behavior of Ammospiza caudacuta and A.
+maritima. By Glen E. Woolfenden. Pp. 45-75, 6 plates, 1 figure. December
+20, 1956.</li>
+
+ <li>The forest habitat of the University of Kansas Natural History
+Reservation. By Henry S. Fitch and Ronald R. McGregor. Pp. 77-127, 2
+plates, 7 figures in text, 4 tables. December 31, 1956.</li>
+
+ <li>Aspects of reproduction and development in the prairie vole
+(Microtus ochrogaster). By Henry S. Fitch. Pp. 129-161, 8 figures in
+text, 4 tables. December 19, 1957.</li>
+
+ <li>Birds found on the Arctic slope of northern Alaska. By James W.
+Bee. Pp. 163-211, plates 9-10, 1 figure in text. March 12, 1958.</li>
+
+ <li>The wood rats of Colorado: distribution and ecology. By Robert B.
+Finley, Jr. Pp. 213-552, 34 plates, 8 figures in text, 35 tables.
+November 7, 1958.</li>
+
+ <li>Home ranges and movements of the eastern cottontail in Kansas. By
+Donald W. Janes. Pp. 553-572, 4 plates, 3 figures in text. May 4,
+1959.</li>
+
+ <li>Natural history of the salamander Aneides hardyi. By Richard F.
+Johnston and Gerhard A. Schad. Pp. 573-585. October 8, 1959.</li>
+			</ol></dd>
+			<dd>More numbers will appear in volume 10.</dd>
+		<dt>Vol. 11.</dt>
+		<dd class="small_margin">
+			<ol class="start_1">
+				<li>The systematic status of the colubrid snake, Leptodeira discolor
+G&uuml;nther. By William E. Duellman. Pp. 1-9, 4 figures. July 14, 1958.</li>
+
+ <li>Natural history of the six-lined racerunner, Cnemidophorus
+sexlineatus. By Henry S. Fitch. Pp. 11-62, 9 figures, 9 tables. September
+19, 1958.</li>
+
+ <li>Home ranges, territories, and seasonal movements of vertebrates
+of the Natural History Reservation. By Henry S. Fitch. Pp. 63-326, 6
+plates, 24 figures in text, 3 tables. December 12, 1958.</li>
+
+ <li>A new snake of the genus Geophis from Chihuahua, Mexico. By John
+M. Legler. Pp. 327-334, 2 figures in text. January 28, 1959.</li>
+
+ <li>A new tortoise, genus Gopherus, from north-central Mexico. By
+John M. Legler. Pp. 335-343. April 24, 1959.</li>
+
+ <li>Fishes of Chautauqua, Cowley and Elk counties, Kansas. By Artie
+L. Metcalf. Pp. 345-400, 2 plates, 2 figures in text, 10 tables. May 6,
+1959.</li>
+
+ <li>Fishes of the Big Blue River Basin, Kansas. By W. L. Minckley.
+Pp. 401-442, 2 plates, 4 figures in text, 5 tables. May 8, 1959.</li>
+
+ <li>Birds from Coahuila, M&eacute;xico. By Emil K. Urban. Pp. 443-516.
+August 1, 1959.</li>
+
+ <li>Description of a new softshell turtle from the southeastern
+United States. By Robert G. Webb. Pp. 517-525, 2 plates, 1 figure in
+text. August 14, 1959.</li>
+			</ol></dd>
+			<dd>Another number will appear in volume 11.</dd>
+		<dt>Vol. 12.</dt>
+		<dd class="small_margin">
+			<ol class="start_1">
+				<li>Functional morphology of three bats: Eumops, Myotis, Macrotus. By
+Terry A. Vaughan. Pp. 1-153, 4 plates, 24 figures in text. July 8,
+1959.</li>
+
+ <li>The ancestry of modern Amphibia: a review of the evidence. By
+Theodore H. Eaton, Jr. Pp. 155-180, 10 figures in text. July 10,
+1959.</li>
+
+ <li>The baculum in microtine rodents. By Sydney Anderson. Pp.
+181-216, 49 figures in text. February 19, 1960.</li>
+			</ol></dd>
+			<dd>More numbers will appear in volume 12.</dd>
+	</dl>
+
+
+
+
+
+
+
+
+<pre>
+
+
+
+
+
+End of the Project Gutenberg EBook of The Baculum in Microtine Rodents, by 
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+Project Gutenberg's The Baculum in Microtine Rodents, by Sydney Anderson
+
+This eBook is for the use of anyone anywhere at no cost and with
+almost no restrictions whatsoever.  You may copy it, give it away or
+re-use it under the terms of the Project Gutenberg License included
+with this eBook or online at www.gutenberg.org
+
+
+Title: The Baculum in Microtine Rodents
+
+Author: Sydney Anderson
+
+Release Date: November 15, 2011 [EBook #38021]
+
+Language: English
+
+Character set encoding: ASCII
+
+*** START OF THIS PROJECT GUTENBERG EBOOK THE BACULUM IN MICROTINE RODENTS ***
+
+
+
+
+Produced by Chris Curnow, Alex Gam, Joseph Cooper and the
+Online Distributed Proofreading Team at http://www.pgdp.net
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+
+
+
+  UNIVERSITY OF KANSAS PUBLICATIONS
+  MUSEUM OF NATURAL HISTORY
+
+  Volume 12, No. 3, pp. 181-216, 49 figs.
+
+  February 19, 1960
+
+  The Baculum in Microtine Rodents
+
+  BY
+  SYDNEY ANDERSON
+
+  UNIVERSITY OF KANSAS
+  LAWRENCE
+  1960
+
+  UNIVERSITY OF KANSAS PUBLICATIONS, MUSEUM OF NATURAL HISTORY
+
+  Editors: E. Raymond Hall, Chairman, Henry S. Fitch,
+  Robert W. Wilson
+
+  Volume 12, No. 3, pp. 181-216, 49 figs.
+  Published February 19, 1960
+
+  UNIVERSITY OF KANSAS
+  Lawrence, Kansas
+
+  PRINTED IN
+  THE STATE PRINTING PLANT
+  TOPEKA, KANSAS
+  1960
+
+[Illustration]
+
+  28-774
+
+
+
+
+The Baculum in Microtine Rodents
+
+BY
+
+SYDNEY ANDERSON
+
+INTRODUCTION
+
+
+Didier (1943, 1954) has described the bacula of several Old World
+microtines, and other rodents. Argyropulo studied (1933a, 1933b) five
+species of Cricetinae and _Microtus socialis_. Ognev (1950) illustrated
+numerous species of Eurasian microtines. Hamilton (1946) figured and
+described the baculum of 11 species of North American microtines. Hibbard
+and Rinker (1942, 1943) figured the baculum of _Synaptomys cooperi
+paludis_ and of _Microtus ochrogaster taylori_. Dearden (1958) studied
+the baculum in two Asiatic species of _Lagurus_, in six subspecies of
+_Lagurus curtatus_ of North America, and in six other species of
+microtines of other genera.
+
+The baculum can be preserved easily with standard study skins, and is
+potentially useful in interpreting relationships on any taxonomic level,
+and especially in determining the relationships of species within a
+genus, if used together with other structures.
+
+The anatomical orientation of the baculum needs comment because some
+confusion exists in the literature, especially concerning the use of the
+terms ventral and dorsal. The urethra lies on the anatomically ventral
+side of the penis, and of the baculum. In the center of the penis lies a
+single corpus cavernosum penis, shown in cross section proximal to the
+baculum in Figure 1c. Dorsally an artery, thinner walled than the ventral
+urethra, ends in a somewhat reticulate sinus surrounding primarily the
+middle part of the baculum within the bulbous glans penis. The corpus
+cavernosum penis (the structure has no median septum, at least distally)
+terminates with the baculum and is closely knit to it. The site of this
+bond is evident in the tuberosities and sculpturing of the base of the
+baculum.
+
+The part of the penis enclosing the baculum, when not erect, is folded
+back as shown in Figures 1a and 1b. As a result the anatomically ventral
+surface faces upwards, or at least posterodorsally. The use of the term
+ventral in this account refers to the anatomically ventral side, that is
+to say to the side of the baculum facing the urethra.
+
+The baculum in microtines consists of an elongate stalk, having a
+laterally, and to a lesser extent dorsoventrally, expanded base and an
+attenuate distal shaft. Usually, three digitate processes of
+cartilaginous material in which additional ossifications may occur arise
+from the terminus of the shaft. The proportions and curvature of the
+stalk vary as do the proportions of the terminal ossifications to each
+other and to the stalk. In some species one or more of the digital
+processes are frequently completely unossified.
+
+[Illustration: FIGURE 1. The baculum in _Microtus
+ochrogaster_--orientation and variation with age. _a._ Diagram of a
+sagittal section of the posterior half of a vole, natural size. The
+penis, containing the baculum (in black), extends ventrally from a point
+posterior to the pubic symphysis (stippled), along the body wall, and
+bends posteriorly at the distal end. _b._ Distal end of penis (x 2)
+showing baculum (in black), the urethra (solid lines) adjacent to the
+baculum, and the corpus cavernosum (broken lines) proximal to the
+baculum. _c._ Oblique view of the cross section of penis (x 4) shown in
+Figure 1 _b_. The thick-walled urethra lies ventral to the curved corpus
+cavernosum. A thinner-walled blood-vessel lies dorsal to the corpus
+cavernosum. The anatomically ventral side of the baculum, in the normal
+non-erect penis shown, is seen to face dorsally. _d._ Graph showing the
+relationship between size of baculum, size of animal, and development of
+digital ossifications. Circles show presence of ossification in stalk
+only; circles enclosing dots indicate presence of secondary ossification
+in median process also; large dots indicate the addition of tertiary
+ossification in one or both of the lateral digitate processes.]
+
+Preserved specimens of _Microtus arvalis_, _Microtus agrestis_, _Microtus
+orcadensis_, _Microtus nivalis_, _Microtus guentheri_, _Microtus
+subterraneus_, _Clethrionomys glareolus_, and _Ellobius lutescens_ were
+provided by Prof. Robert Matthey of Lausanne, Switzerland. J. Knox Jones,
+Jr. carefully saved the bacula with specimens of _Microtus fortis_ and
+_Clethrionomys rufocanus_ from Korea. Dr. W. B. Quay, Department of
+Zoology, University of California, supplied specimens of _Synaptomys
+cooperi_, _Phenacomys intermedius_, and _Microtus oregoni_. Dr. Franklin
+Sturges and Mr. John W. Goertz, Museum of Natural History, Oregon State
+College, Corvallis, have provided specimens including bacula of
+_Clethrionomys occidentalis_, _Microtus oregoni_, and _Microtus
+townsendii_. Dr. Randolph L. Peterson and Mr. Bristol Foster, Royal
+Ontario Museum of Zoology, Toronto, Canada, provided specimens of
+_Phenacomys intermedius_. Dr. J. N. Layne, University of Florida,
+Gainsville, Florida, presented me with a baculum of _Microtus parvulus_.
+
+I am indebted to all of these persons for their aid, and to various
+collectors for the Museum of Natural History, who preserved bacula with
+specimens. Many of these specimens were obtained through the assistance
+of the University of Kansas Endowment Association and the National
+Science Foundation.
+
+
+
+
+METHODS
+
+
+Bacula were obtained from fresh specimens, specimens preserved in alcohol
+or formalin, and dried study skins. The processing of bacula has been
+discussed by Hamilton (1946), Friley (1947), White (1951), and Dearden
+(1958). The methods used to preserve bacula for my study differed some
+from any of those reported. The terminal part of each penis including the
+baculum imbedded in the glans penis was removed in its entirety and
+placed in a vial. The catalogue number was kept with each specimen at all
+times. A two per cent solution of potassium hydroxide was added. All
+specimens were examined at least once a day. If tissues other than the
+glans penis were present they were removed with forceps when softened
+usually at the end of one day. Several drops of Alizarin red-S stain in a
+saturated alcoholic solution were added to the 3 to 5 ccs. of KOH
+solution in each vial. Solutions were replaced if they became turbid
+enough to obstruct observation of the clearing penis. After one day the
+solution containing stain was removed and replaced with two per cent KOH
+solution without stain. When the glans became sufficiently cleared that
+the stained baculum could be seen easily, the solution was replaced by
+glycerin in which clearing was completed. The time required for the
+entire process varied from one day to more than two weeks depending on
+the size of the specimen and on its condition. Fresh specimens clear more
+rapidly than dried specimens, and those that are dried more rapidly than
+those that are preserved. A three or four per cent solution of hydroxide
+will hasten the process, but more frequent observation is required to
+prevent excessive maceration.
+
+Specimens were then examined in a shallow dish containing glycerin under
+a binocular microscope. The baculum can be viewed from any desired
+direction. The method described above leaves the baculum intact within
+the glans penis; therefore its orientation can be determined relative to
+the thick walled urethra and the thin walled dorsal artery that extends
+onto the dorsal side of the baculum. The ventral curvature of the penis
+proximal to the baculum, and the distal extension, characteristic of most
+species, of the dorsal border of the glans (both shown in Figure 1) are
+other features aiding in correctly orienting cleared specimens. The
+digitate processes are not so often injured, lost, or displaced when the
+method described above is used as they are when the penis is dissected.
+Specimens were stored in glycerin in glass shell vials having
+polyethylene stoppers. A small card bearing the name, number, locality,
+and other data was placed in each vial. A specimen thus enclosed can be
+kept indefinitely, or removed and mounted in balsam as described by White
+(1951:631) or in plastic as described by Dearden (1958:541) and thus
+stored in the vial containing the skull of the specimen.
+
+Drawings were made on millimeter ruled paper while the baculum was viewed
+under a binocular microscope with a square ruled eyepiece.
+
+Unless otherwise noted all specimens listed are in the University of
+Kansas Museum of Natural History. Catalogue numbers are cited.
+Measurements are accurate to within less than one-tenth of a millimeter.
+Proportions as stated in the text are approximations, accurate to within
+one-twelfth (8.33 per cent). The range of variation is unknown for some
+species. Mention is made if maturity is known or suspected to differ in
+specimens being compared.
+
+The development of the baculum has been studied by Callery (1951) in
+_Mesocricetus auratus_ and by Ruth (1934) in the laboratory rat. In the
+rat (_Rattus norvegicus_) the bone is of endoblastemal origin being laid
+down by a condensation of undifferentiated mesenchymal cells. At the
+distal end of the bone dense fibrous tissue is then differentiated and at
+the proximal end hyaline cartilage. Growth is by substitution at the
+proximal end and by subperiosteal lamellation circumferentially. A marrow
+cavity is formed by resorption. In the baculum of the hamster the primary
+center of ossification is in the stalk, and is present at the age of
+three days; the secondary centers are in lateral processes and are
+present at 80 days and enlarge subsequently. A tertiary center, in each
+median process, may or may not develop later. Maximum development of the
+baculum is reached late in the reproductive life of the hamster.
+
+The early ossification of the baculum noted in the rat and the hamster
+occurs in _Microtus_ also. A specimen of _Microtus montanus fusus_
+(76831, from 5 mi. N, 26 mi. W Saguache, 9600 ft., Saguache County,
+Colorado) only 74 mm. in total length and weighing only 6.6 grams, had a
+slender ossified baculum having enlarged ends. This vole was one-half of
+the average length and less than one-fifth of the average weight of an
+adult, and of approximately the size at which weaning takes place.
+
+The development of the baculum in _Microtus ochrogaster_ was studied in
+32 specimens of various ages. The specimens (between Nos. 74994 and
+75074) were collected between August 15 and September 4, 1957, at
+localities on the Great Plains. These specimens were from breeding
+populations, as evidenced by pregnancy of females and by large size of
+testes of males. The length and width of the stalk of the baculum, the
+presence of digital ossifications, the total length of the animal, and
+the size of the testes were noted. Variability in length of testes is
+greatest when voles are from 140 to 150 mm. in total length. Sexual
+maturity is reached rather abruptly when the total length of most
+individuals is 140 to 150 millimeters. If the baculum likewise underwent
+more rapid growth at the onset of sexual maturity, greater variability
+should be evident in the length of the baculum of voles 140 to 150 mm. in
+total length than in bacula of voles of other sizes. This was the case
+(see Figure 1d). The baculum does not, however, suddenly reach its
+maximum maturity.
+
+The primary ossification is in the stalk. The secondary ossification is
+in the median process except in _Lagurus_ (Dearden, 1958:551) and some
+individuals of _Neofiber_ (see account on page 258). Tertiary centers of
+ossification are in the lateral processes. The primary ossification is
+present at an early age and subsequently increases in size and solidity.
+The secondary and tertiary ossifications are progressively more common in
+older voles. The increase in degree of ossification of all parts
+continues after sexual maturity is reached. Individual variation and
+variation with age in the baculum of _Microtus pennsylvanicus_ have been
+illustrated by Hamilton (1946:380). Figures 14, 15, and 17 illustrate
+variation with size, which is correlated with age, and also illustrate
+individual variation. The three bacula are from adult voles having testes
+that measured 15, 16 and 16 mm. in length, respectively. Each vole was
+trapped in late June. The total lengths in millimeters of the three voles
+are 172, 167, and 181; weights are 55, 52.4, and 65.5 grams. I judge that
+the greater size of the stalk and the better developed base shown in
+Figure 17 than in Figure 15 are illustrative of age variation; the
+difference in the size of the lateral digitate processes is, in this
+case, attributable to individual variation. Differences in the distal end
+of the baculum in Figures 42 and 43, show individual variation also.
+Figures 35 and 36 represent two different subspecies; different
+individuals of _M. mexicanus mogollonensis_, however, exhibit individual
+variation of the same degree.
+
+Hall and Cockrum (1953) list 44 species of microtines in North America.
+At least twelve of these are insular or local forms perhaps derived from
+some other species; for example _Microtus coronarius_, an insular form
+derived from _Microtus longicaudus_; _Microtus provectus_, considered by
+Chamberlain (1954:587) and by Wheeler (1956:176) as a subspecies of
+_Microtus pennsylvanicus_; and _Microtus ludovicianus_, a close relative
+of _Microtus ochrogaster_.
+
+All North American genera have been studied. Of the genus _Microtus_ in
+North America, all subgenera but _Orthriomys_ and all species but the
+following nine, have been studied: _M. (Orthriomys) umbrosus_, the
+insular _M. (Stenocranius) abbreviatus_, _M. (Microtus) breweri_, _M.
+(Microtus) nesophilus_, _M._
+
+[Illustration: FIGURES 2-13. Bacula of microtines. Unless indicated
+otherwise views are (_a_) of the dorsum, (_b_) the right side, and (_c_)
+the proximal end with the dorsal surface upward. Exact localities are
+given in accounts of species concerned.
+
+2. _Lemmus trimucronatus_, 50678, Point Barrow, Alaska.
+
+3. _Dicrostonyx groenlandicus_, 50539, Porcupine Lake, Brooks Range,
+Alaska.
+
+4. _Dicrostonyx groenlandicus_, 52524, Point Barrow, Alaska.
+
+5. _Synaptomys cooperi saturatus_, WBQ 3-C-454, 3 mi. S Demotte, Indiana.
+
+6. _Synaptomys cooperi paludis_, 13716, Meade County State Park, Kansas.
+
+7. _Phenacomys intermedius celatus_, SA 2044, Quebec.
+
+8. _Phenacomys intermedius intermedius_, WBQ 3-C-309, 5.4 mi. S Moran,
+Teton Co., Wyoming.
+
+9. _Clethrionomys rufocanus_, 60438, 1 mi. NW Oho-ri, Korea, (_d_)
+ventral view.
+
+10. _Clethrionomys gapperi_, 42108, 31 mi. N Pinedale, Wyoming.
+
+11. _Clethrionomys rutilus_, 42865, 5 mi. NNE Gulkana, Alaska.
+
+12. _Clethrionomys occidentalis_, FWS 30, Mary's Peak, Benton Co.,
+Oregon.
+
+13. _Clethrionomys glareolus_, 67100, Zermatt, Valais, Switzerland.]
+
+[Illustration: FIGURES 14-25. Bacula of _Microtus_. Unless indicated
+otherwise views are (_a_) of the dorsum, (_b_) the right side, and (_c_)
+the proximal end with dorsal surface upward.
+
+14. _M. pennsylvanicus_, 42439, 1 mi. S, 2 mi. E Eagle Nest, Colfax Co.,
+New Mexico; abnormality perhaps owing to injury; dorsal view.
+
+15. _M. pennsylvanicus_, 42306, 5 mi. N, 26 mi. W Saguache, Colorado;
+dorsal view.
+
+16. _M. pennsylvanicus_, 43043, 20 mi. NE Anchorage, Alaska, ventral
+view.
+
+17. _M. pennsylvanicus_, 42430, 1 mi. S, 2 mi. E Eagle Nest, New Mexico.
+
+18. _M. agrestis_, 67102, Gryon, Switzerland.
+
+19. _M. montanus amosus_, 62241, 1/2 mi. E Soldier Summit, Wasatch Co.,
+Utah.
+
+20. _M. montanus nanus_, 57470, 2 mi. N, 2 mi. W Pocatello, Idaho.
+
+21. _M. montanus fusus_, 42307, 5 mi. N, 26 mi. W Saguache, Colorado.
+
+22. _M. arvalis_, 67101, Vidy, Switzerland, possibly not mature.
+
+23. _M. guentheri_, 67104, Palestine.
+
+24. _M. orcadensis_, 67106, Orkney Islands, orientation uncertain.
+
+25. _M. fortis_, 63841, Chipo-ri, Korea, (_d_) ventral view.]
+
+[Illustration: FIGURES 26-39. Bacula of microtines. Unless indicated
+otherwise views are (_a_) of the dorsum, (_b_) the right side, and (_c_)
+the proximal end with the dorsal surface upward.
+
+26. _M. (Pitymys) fatioi_, 67103, Zermatt, Switzerland, immature.
+
+27. _M. (Pitymys) pinetorum_, 76834, 2 mi. N Baldwin, Douglas Co.,
+Kansas.
+
+28. _M. (Pitymys) pinetorum_, 68545, 1 mi. NE Pleasant Grove, Kansas.
+
+29. _M. (Pitymys) quasiator_, 30709, Teocelo, Veracruz, (_d_) ventral
+view.
+
+30. _M. (Pitymys) quasiator_, 19878, 5 km. N Jalapa, Veracruz.
+
+31. _M. (Pedomys) ochrogaster_, 75036, 1 mi. N, 2 mi. E Oberlin, Kansas.
+
+32. _M. (Stenocranius) miurus_, 51152, Lake Schrader, Brooks Range,
+Alaska.
+
+33. _M. (Stenocranius) miurus_, 51169, Lake Schrader, Brooks Range,
+Alaska.
+
+34. _M. (Stenocranius) gregalis_, 8059, "Eastern Europe."
+
+35. _M. mexicanus mexicanus_, 63094, Valle de Bravo, Estado de Mexico,
+Mexico.
+
+36. _M. mexicanus mogollonensis_, 63298, Mt. Taylor, Valencia Co., New
+Mexico.
+
+37. _M. californicus_, 76828, 1 mi. NE Berkeley, California; (_d_)
+ventral view.
+
+38. _M. (Arvicola) richardsoni_, 42454, 31 mi. N Pinedale, Sublette Co.,
+Wyoming.
+
+39. _M. richardsoni_, 37903, 23-1/2 mi. S, 5 mi. W Lander, Wyoming;
+distal end.]
+
+[Illustration: FIGURES 40-49. Bacula of microtines. Unless indicated
+otherwise views are (_a_) of the dorsum, (_b_) the right side, and (_c_)
+the proximal end with the dorsal surface upward.
+
+40. _Microtus (Pitymys) parvulus_, UF 1508, 1 mi. W Micanopy, Florida.
+
+41. _Microtus townsendii_, 79186, Sec. 33, T. 11S, R. 5W, Benton Co.,
+Oregon.
+
+42. _Microtus (Herpetomys) guatemalensis_, 65895, 2 mi. S San Juan Ixcoy,
+Guatemala.
+
+43. _M. guatemalensis_, 65921, 10 mi. E, 4 mi. S Totonicapan, Guatemala,
+dorsal view of tip.
+
+44. _Microtus oeconomus_, 43048, Kelsall Lake, British Columbia.
+
+45. _Microtus (Chilotus) oregoni_, WBQ 3-C-248, 5 mi. N Orick,
+California.
+
+46. _Lagurus (Lemmiscus) curtatus_, 26053, 9 mi. S Robertson, Uinta Co.,
+Wyoming.
+
+47. _Microtus (Chionomys) nivalis_, 65127, Wetterstein, Germany,
+orientation uncertain.
+
+48. _Microtus (Chionomys) longicaudus_, 50253, Crane Flat, Mariposa Co.,
+California.
+
+49. _Neofiber alleni_, 27268, 2 mi. S Gainesville, Florida, orientation
+uncertain.]
+
+(_Microtus_) _provectus_ (the last three are probably insular derivatives
+of _M. pennsylvanicus_), _M._ (_Microtus_) _fulviventer_ (perhaps derived
+from the same stock as _Microtus mexicanus_), _M._ (_Microtus_)
+_xanthognathus_ (perhaps related to _Microtus chrotorrhinus_), _M._
+(_Microtus_) _coronarius_, and _M._ (_Pedomys_) _ludovicianus_.
+
+
+SPECIES OF WHICH BACULA WERE EXAMINED
+
+  Subfamily: Microtinae                              Number of Specimens
+    Tribe: Lemmi
+      _Dicrostonyx groenlandicus_ (Traill)                   4
+      _Lemmus trimucronatus_ (Richardson)                    6
+      _Synaptomys cooperi_ Baird                             5
+    Tribe: Microti
+      Genus: _Clethrionomys_ Tilesius, 1850
+        _Clethrionomys rutilus_ Pallas                       4
+        _Clethrionomys gapperi_ (Vigors)                     9
+        _Clethrionomys occidentalis_ (Merriam)               1
+        _Clethrionomys glareolus_ Schreber                   1
+        _Clethrionomys rufocanus_ Sundevall                  1
+      Genus: _Phenacomys_ Merriam, 1897
+        _Phenacomys intermedius_ Merriam                     5
+      Genus: _Ondatra_ Link, 1795
+        _Ondatra zibethicus_ (Linnaeus)                      1
+      Genus: _Microtus_ Schrank, 1798
+        (_Herpetomys_) _guatemalensis_ Merriam               3
+        (_Arvicola_) _richardsoni_ (DeKay)                   2
+        (_Chilotus_) _oregoni_ (Bachman)                     3
+        (_Stenocranius_) _gregalis_ (Pallas)                 1
+        (_Stenocranius_) _miurus_ Osgood                     9
+        (_Chionomys_) _longicaudus_ (Merriam)                6
+        (_Chionomys_) _nivalis_ Martins                      2
+        (_Microtus_) _arvalis_ (Pallas)                      1
+        (_Microtus_) _orcadensis_ Millais                    1
+        (_Microtus_) _guentheri_ Danford and Alston          1
+        (_Microtus_) _fortis_ Buechner                        2
+        (_Microtus_) _montanus_ (Peale)                     15
+        (_Microtus_) _townsendii_ (Bachman)                  3
+        (_Microtus_) _oeconomus_ (Pallas)                   10
+        (_Microtus_) _mexicanus_ (Saussure)                 13
+        (_Microtus_) _californicus_ (Peale)                  2
+        (_Microtus_) _pennsylvanicus_ (Ord)                 13
+        (_Microtus_) _agrestis_ (Linnaeus)                   1
+        (_Pedomys_) _ochrogaster_ (Wagner)                  41
+        (_Pitymys_) _pinetorum_ (LeConte)                    2
+        (_Pitymys_) _parvulus_ (Howell)                      1
+        (_Pitymys_) _quasiater_ (Coues)                      5
+        (_Pitymys_) _fatioi_ Mottaz                          1
+      Genus: _Neofiber_ True, 1884
+        _Neofiber alleni_ True                               2
+      Genus: _Lagurus_ Gloger, 1841
+        _Lagurus curtatus_ (Cope)                            7
+
+           Total number examined                           184
+
+
+
+
+ACCOUNTS OF SPECIES
+
+
+Dicrostonyx groenlandicus (Traill)
+
+Figs. 3 and 4
+
+Baculum: stalk elongate, greatest length (3.1 mm.) 2-1/5 to 2-1/2 times
+greatest breadth, and 4-1/2 times greatest depth; digitate processes
+usually cartilaginous, occasionally lateral processes partly ossified;
+basal tuberosities weakly to moderately developed, medially confluent;
+posterior profile in dorsal view rounded with rounded posterior apex or
+shallow notch; dorsal concavity in end-view shallower and not so wide as
+ventral concavity; median constriction approximately 2/3 greatest depth;
+ventral part of base in end-view wider than dorsal part; shaft straight
+or slightly curved; base of stalk placed dorsally relative to axis of
+shaft; stalk spatulate, sometimes with distal enlargement; at mid-point
+stalk wider than high; lateral profile in dorsal view sloping gradually
+without abrupt curvature anterior to point of greatest width.
+
+The baculum of _Dicrostonyx torquatus_ figured by Ognev (1948:476) agrees
+with that of _D. groenlandicus_ in shape of stalk, and in lateral
+digitate processes that are small relative to size of median process; but
+differs in more elongate, terminally enlarged, bulbar shape of median
+process. None of my specimens showed ossification in the lateral
+processes, observed by Hamilton (1946:381) in _Dicrostonyx rubricatus
+richardsoni_ [ = _D. groenlandicus richardsoni_]. In all of my specimens
+the cartilaginous median process was larger than that figured by
+Hamilton, or by Dearden (1958:542).
+
+_Specimens examined_: Four from; Point Barrow, Alaska, 52524 (Barrow
+Village), 67264 (died in captivity); Brooks Range, Alaska, 50536 (Wahoo
+Lake, 69 deg.08', 146 deg.58'), 50539 (Porcupine Lake, 68 deg.51'57", 146 deg.29'50",
+3140 ft.).
+
+
+Lemmus trimucronatus (Richardson)
+
+Fig. 2
+
+Baculum: Stalk heavy, broad, greatest length (2.8 mm.) in mature
+individuals (Fig. 2) as little as 1-1/3 times greatest breadth, greatest
+length no less than 2-2/3 times greatest depth of base; three ossified
+processes, median one from as long as to 1/2 longer than the lateral
+processes, and approximately 2/3 wider and twice as deep as lateral
+processes; length of median process almost 3-1/2 times its breadth,
+approximately 1/2 length of stalk; basal fossae broadly confluent;
+posterior profile in dorsal view evenly rounded; in end-view ventral
+concavity deeper than dorsal concavity, constriction as little as 1/2
+greatest depth in mature specimens; shaft straight, bluntly rounded, or
+slightly decurved and laterally inflated terminally; lateral profile in
+dorsal view a gradual slope from widest point of stalk anteriorly onto
+shaft; in younger individuals stalk slenderer, otherwise as described
+above.
+
+Five specimens examined by me differ from one figured and described by
+Hamilton (1946:379) in that stalk is better developed, larger relative to
+size of processes, length of stalk in my specimen (Fig. 2) 2.8 as opposed
+to 2.1 mm. in Hamilton's specimen; median process shorter, 1.5 as opposed
+to 1.8 mm., proximal end rounded rather than concave, not partially
+enclosing tip of shaft; proportion of and relative sizes of median and
+lateral processes approximately same as in Hamilton's _Lemmus helvolus_
+[ = _Lemmus trimucronatus helvolus_]. A specimen figured by Dearden
+(1958:542) has a basally trilobed median process.
+
+The baculum of the Asiatic _Lemmus lemmus_ figured by Ognev (1948:413)
+agrees with my specimens in the ossification of three processes, the
+relative sizes of these processes to each other and to the stalk, the
+well-developed base of the stalk and heavy bluntly rounded shaft; the
+baculum of _Lemmus lemmus_ differs in greater anterolateral extent of
+basal tuberosities, in proximal notch seemingly separating these
+tuberosities, and in median process being slenderer.
+
+_Specimens examined_: Five, of two subspecies; _Lemmus trimucronatus
+alascensis_, Point Barrow, Alaska, numbers 50591, 50678, 50731, 50758;
+_Lemmus trimucronatus subarcticus_, Wahoo Lake, 69 deg.08', 146 deg.58', 2350
+ft., Brooks Range, Alaska, 50948.
+
+
+Synaptomys cooperi Baird
+
+Figs. 5 and 6
+
+Baculum: Stalk elongate, greatest length (2.7 to 2.8 mm.) 2-1/3 to 2-1/2
+times greatest breadth, 4 to 5 times greatest depth; three processes
+ossified or lateral processes unossified, ossifications relatively small
+(in 78380, median ossification less than 1/4 as large as lateral
+ossifications although median cartilaginous process is larger), length of
+median process 1/5 to 1/6 of length of stalk, cartilaginous part of
+median process larger; posterior profile in dorsal view convex throughout
+or bilobate; tuberosities moderately developed, deflected dorsal to axis
+of shaft; in end-view medial construction 3/5 greatest depth of
+tuberosities; shaft tapered from point of greatest width, slightly
+inflated terminally.
+
+The specimen (KU 13716) figured by Hibbard and Rinker (1942:29) has been
+restudied. It was first cleared and stained to soften the dry cartilage
+binding the digital processes together and to differentiate bone and
+cartilage. The lateral processes are small and cartilaginous (Fig. 6) and
+seem intact. The differences between this specimen and others examined by
+Hamilton (1946:381), Dearden (1958:542), and myself, namely the
+relatively larger median ossification, the absence of ossification in
+lateral processes, and the distinctly bilobate base and larger size, may
+represent geographic differences, or individual variation. The
+proportions of length, width, and depth of the stalk, and the appearance
+in lateral view do not differ greatly from others examined by Hamilton,
+by Dearden (1958:546), and by me.
+
+_Specimens examined_: Five, representing four subspecies; _S. cooperi
+gossii_, 6 mi. N Midway, Holt Co., Nebraska 78379, 78380; _S. cooperi
+relictus_, 5 mi. N, 2 mi. W Parks, Dundy Co., Nebraska, 72601 (immature);
+_S. cooperi saturatus_, 3 mi. S Demotte, Jasper Co., Indiana, 3-C-454,
+collection of W. B. Quay; _S. cooperi paludis_, Meade County State Park,
+Kansas, 13716.
+
+
+Clethrionomys rutilus Pallas
+
+Fig. 11
+
+Baculum: Stalk elongate, and proximally enlarged, greatest length (2.7
+mm.) 2 times greatest breadth; less than 4 times greatest depth; three
+well-developed ossified processes; length of stalk 2-1/3 times length of
+median process; median process with basal (and ventral) protuberence and
+lateral lobes, arched in dorsoventral plane; lateral processes as large
+as median process, flattened distally, having ventromedial vane on distal
+half; basal tuberosities of stalk well developed, medially confluent;
+posterior profile in dorsal view trilobate or convex throughout with
+rounded posterior apex; dorsal concavity well developed, ventral surface
+but slightly concave, medial constriction of base as little as 1/2
+greatest depth; shaft straight, slender, at mid-point of stalk but
+slightly wider than high; basal tuberosities largely dorsal to axis of
+shaft in lateral view; lateral profile in dorsal view with an abrupt
+curvature separating the gently sloping sides of the shaft from the basal
+part at its greatest breadth.
+
+The specimen of _Clethrionomys rutilus_ figured by Ognev (1950:120) is
+essentially like the North American specimens examined by me in the
+relative sizes of the ossifications and the general shape of the stalk.
+
+_Specimens examined_: Four, of one subspecies; _C. r. dawsoni_, west bank
+Gakona River, 1700 ft., 5 mi. NNE Gulkana, Alaska, 42865, 42866; SW end
+Dezadeash Lake, 2400 ft., Yukon Territory, 42910, 42921.
+
+
+Clethrionomys gapperi (Vigors)
+
+Fig. 10
+
+Baculum: Stalk elongate, greatest length (2.8 mm.) 1-3/4 times greatest
+breadth, and 3-3/4 times greatest depth; proximally enlarged, greatest
+depth 1/2 greatest breadth; three well-developed ossified processes;
+length of stalk 2-1/3 times length of median process; median process
+arched in dorsoventral plane, with basiventral protuberence or spine and
+lateral lobes; lateral processes as large as median process, flattened
+distally, arched; basal tuberosities of stalk well developed, medially
+confluent; posterior profile in dorsal view trilobate or convex
+throughout with a rounded posterior apex; dorsal concavity well
+developed, ventral surface but slightly concave, or in some cases
+slightly convex; medial constriction of base 3/5 greatest depth; shaft
+straight, slender, at mid-point of stalk twice as wide as high; basal
+tuberosities dorsally placed relative to axis of shaft; lateral profile
+in dorsal view abruptly curved anterior to point of greatest width;
+slender stalk distinct from angular enlarged base.
+
+The most noticeable difference between the baculum of _C. rutilus_ and
+_C. gapperi_ is size. The proportions of the four ossifications are
+approximately the same. Ventral vanes on the lateral processes are not
+developed in _C. gapperi_. _C. gapperi_ and _C. rutilus_ are more nearly
+alike in their bacula than any other two species of _Clethrionomys_
+examined. _Clethrionomys occidentalis_, the other New World species, is
+also much like _C. gapperi_ and _C. rutilus_. The differences are of a
+magnitude comparable to those between the bacula in subspecies of
+_Microtus montanus_ (Figs. 19-21) for example, or in subspecies of
+_Lagurus curtatus_ (Dearden, 1958:542).
+
+_Specimens examined_: Nine, of two subspecies; _Clethrionomys gapperi
+athabascae_, British Columbia, 42922 (Indian Creek, Mile Post 234 of
+Alaskan Highway), 64281 (West bank Racing River, 89 mi. W Muskwa), 64287
+(North bank Tetsa River, 56 mi. W, 11 mi. S Muskwa), 64290 (44 mi. W, 9
+mi. S Muskwa), 64310 (32 mi. W, 2 mi. S Muskwa); _Clethrionomys gapperi
+galei_, 31 mi. N Pinedale, Sublette Co., Wyoming, 42108; Grand Mesa,
+Delta Co., Colorado, 60014 and 60015 (5-1/2 mi. E, 12 mi. S Collbran),
+60022 (8 mi. E, 1/2 mi. S Skyway).
+
+
+Clethrionomys occidentalis (Merriam)
+
+Fig. 12
+
+Baculum: Stalk elongate, greatest length (2.8 mm.) 2-1/2 times greatest
+breadth, 6 times greatest depth; three well-developed ossified processes;
+median process larger than lateral processes, 1/2 the length of stalk,
+curved, basally broad, ventrally keeled, trilobate posteriorly; lateral
+ossifications large, flattened distally, curved; posterior profile of
+stalk posteriorly slightly emarginate, thus bilobate in outline; in
+end-view dorsal concavity deeper than ventral, constriction less than 1/2
+greatest depth, tuberosities confluent, visible in dorsal view at each
+side; shaft slender, especially in depth, straight; at mid-point of stalk
+almost twice as wide as deep, slight terminal inflation.
+
+The general proportions of the stalk and the relatively large, uniquely
+shaped processes, are characteristic of most specimens of the genus
+_Clethrionomys_ examined.
+
+_Specimen examined_: _C. occidentalis californicus_, one from Mary's
+Peak, Benton Co., Oregon, 30, F. W. Sturges' collection.
+
+
+Clethrionomys glareolus Schreber
+
+Fig. 13
+
+Baculum: Stalk elongate, greatest length (2.9 mm.) twice the greatest
+breadth in the specimen examined, flattened proximally, greatest length
+almost 6 times greatest depth of base; three well-developed ossified
+processes; median process arched in a dorsoventral plane, with basal
+notch and lateral lobes; lateral processes as long as median process,
+bowed in dorsal view, flattened distally, with ventromedial vane; basal
+tuberosities of stalk weakly developed, medially confluent; posterior
+profile in dorsal view evenly rounded; in end-view dorsal concavity
+shallow in comparison to most species but deeper than ventral concavity,
+constriction 3/4 greatest depth; shaft straight, at mid-point slightly
+wider than high, elongate, widest point of stalk less than 1/4 of total
+length from proximal end, slight lateral inflation at tip; lateral
+profile in dorsal view sloping at first abruptly and then gradually from
+widest point of stalk anteriorly onto shaft.
+
+The specimen of _Clethrionomys glareolus_ figured by Ognev (1950:31) in
+dorsal view as I interpret it, resembles my specimen in the rounded base;
+in the elongate, distally inflated shaft; in the initially abrupt slope
+of the lateral profile in dorsal view from the greatest width of stalk
+anteriorly; and in the presence of three well ossified processes. Ognev's
+specimen differs from mine in the median process being more elongate
+relative to its width, and rounded proximally, lacking lateral lobes and
+basal notch; in lateral processes being less curved; in the greater
+terminal inflation of the shaft; and in the closer approximation of the
+terminal processes to the shaft. The baculum of _Clethrionomys glareolus_
+as described and figured by Didier (1954:243-244) resembles my specimen
+in general proportions, but is more pointed proximally and more curved in
+dorsoventral plane. Didier states that the baculum is rather variable in
+form in this species, in different regions, but that a large number of
+specimens must be examined to assess the geographic nature of this
+variation.
+
+_Specimen examined_: One from Zermatt, Valais, Switzerland, 67100.
+
+
+Clethrionomys rufocanus Sundevall
+
+Fig. 9
+
+Baculum: Base of stalk broad but relatively flattened dorsoventrally,
+greatest length (3.2 mm.) less than 1-1/2 greatest width, 4 times
+greatest depth; three well-developed ossified processes; median process
+arched in dorsoventral plane, having basal notch and lateral lobes;
+lateral processes as long as median process, flattened distally, with
+ventromedial vane; basal tuberosities of stalk weakly developed, medially
+confluent; posterior profile in dorsal view convex with rounded posterior
+apex; dorsal surface of base almost flat, ventral concavity broad and
+shallow; constriction 3/4 greatest depth (not including an unusual
+irregularity on the ventral surface of the base); shaft straight, at
+mid-point of stalk distinctly wider than high, slender at distal end,
+widest point of stalk almost 1/3 of total length from proximal end, tip
+of shaft rounded; lateral profile in dorsal view gradually sloping from
+widest point anteriorly onto shaft.
+
+The specimen of _Clethrionomys rufocanus_ figured by Ognev (1950:97)
+resembles my specimen in the presence of three well ossified processes.
+Ognev's specimen differs however in the lack of a proximal notch on the
+median process, the lesser proportion of the stalk included in the basal
+enlargement, the more posterior position of the point of greatest width,
+and the presence of a concavity in the posterior profile of the stalk in
+dorsal view. These differences in the stalk may be owing to a difference
+in age (my specimen perhaps being older).
+
+_Specimen examined_: One from 1 mi. NW Oho-ri, 6 M., Korea, 60438.
+
+
+Phenacomys intermedius Merriam
+
+Figs. 7 and 8
+
+Baculum: Stalk slender, greatest length (2.9 mm.) 2-1/4 to 2-1/2 times
+greatest breadth, 4 times greatest depth; three well-developed ossified
+processes, median one almost 1/2 length of stalk, curved, broad basally
+and slightly larger in all dimensions than either lateral process;
+lateral processes flattened distally, curved; base of stalk well
+developed, basal tuberosities medially confluent or separated by medial
+emargination, posterolateral faces flattened or rough; emarginations in
+the four adults examined; posterior profile in dorsal view bluntly
+pointed or flattened except for emargination posterially, abruptly curved
+at point of greatest width; shaft arising broadly from distal side of
+base of stalk; in end-view hour-glass shaped, medial constriction
+pronounced, both dorsal and ventral concavities deep; shaft having
+relatively straight but distally convergent sides; at mid-point of stalk,
+1 to 1-1/2 times as wide as deep; tip bluntly rounded, or slightly
+inflated.
+
+The specimens from Quebec differ from the one from Wyoming in smaller
+size, relatively smaller lateral digital processes, larger more medial
+basal emargination, and slender shafts. The baculum of _Phenacomys
+intermedius_ differs much from that of _Phenacomys longicaudus_,
+described by Hamilton (1946:381) and by Dearden (1958:547). Dearden
+states that the three bacula examined by him of _Phenacomys longicaudus_
+differ markedly from the specimen described by Hamilton. It seems to me
+that in major features the resemblance is greater between the specimens
+of _Phenacomys longicaudus_ examined by these two authors than between
+their specimens and specimens of other microtines, including _Phenacomys
+intermedius_. Neither Hamilton nor Dearden record the exact localities of
+capture, the collections in which the specimens are deposited, or the
+catalogue numbers of specimens. Consequently verification of
+identifications and observations is difficult.
+
+_Specimens examined_: Five, of two subspecies; _P. intermedius
+intermedius_, 5.4 mi. S Moran, Teton Co., Wyoming, 3-C-309, collection of
+W. B. Quay; _P. intermedius celatus_, four (including one immature
+specimen) from Authiernord, Abitibi-ouest Co., Quebec, specimens in
+collection of Bristol Foster designated by numbers 2041-2044 of S.
+Anderson's field catalogue. Smith and Foster (1957:107) were of the view
+that _Phenacomys ungava_ (including the above specimens from Quebec) may
+be specifically distinct from _Phenacomys intermedius_.
+
+
+Ondatra zibethicus (Linnaeus)
+
+Not figured
+
+Baculum: In the single specimen examined, less mature than that figured
+by Hamilton (1946:384), the digitate processes are cartilaginous, the
+basal tuberosities are less well developed, and the shaft is slenderer
+throughout. The cartilaginous processes are of the same proportions as
+ossified processes in the figure mentioned. The shaft is also convex
+ventrally in lateral profile. The view of the side here considered to be
+anatomically the ventral side (adjacent to the urethra) is labelled
+dorsal view in Hamilton's specimen.
+
+_Specimen examined_: One, from Reserve, Brown Co., Kansas, 72405.
+
+
+Microtus (Herpetomys) guatemalensis Merriam
+
+Figs. 42 and 43
+
+Baculum: Stalk moderately elongate, greatest length (3.5 mm.) 2-1/3 times
+greatest breadth, spatulate, flattened throughout, greatest thickness 1/3
+millimeter; three ossified processes; median process having three
+cornered base, curved dorsally, wider than high, 1/4 to 1/5 greatest
+length of stalk; each lateral process bent at middle, as long as median
+process, compressed laterally; base of stalk curved dorsally,
+tuberosities marginal, hence narrow, lateral excavations of tuberous
+margin not confluent medially; in end-view ventral concavity broad, no
+dorsal concavity, medial constriction but slightly less than greatest
+thickness (not depth); shaft wider than high throughout, at mid-point
+more than 3 times as wide as high; tip of shaft slightly inflated both
+laterally and dorsoventrally; lateral profile gradually sloping
+anteriorly from widest point of stalk.
+
+Specimen number 65921 (Fig. 43) differs from number 65895 (Fig. 42)
+described above. Terminus of shaft of number 65921 has lateral lobes from
+which arise lateral cartilaginous processes; median terminal ossification
+irregular in shape, smaller, imbedded in terminally bilobate cartilage.
+In the spatulate flattened stalk these two specimens are much alike. An
+immature specimen, number 65908, is smaller (length of stalk 2.6 mm.)
+also flattened and spatulate, has the terminal processes cartilaginous,
+the lateral processes bent medially, and proportions as in the adult.
+
+The baculum shows no noteworthy resemblance to that of any other species
+of North American _Microtus_; on the other hand the differences between
+_M. guatemalensis_ and some other species are no greater than the
+differences between certain species included in the subgenus _Microtus_.
+The baculum neither strengthens nor weakens the case for subgeneric rank
+for _M. (Herpetomys) guatemalensis_.
+
+_Specimens examined_: Three from Guatemala; 65895 (2 mi. S San Juan
+Ixcoy), 65908, (3-1/2 mi. SW San Juan Ixcoy), 65921 (10 mi. E, 4 mi. S
+Totonicapan).
+
+
+Microtus (Arvicola) richardsoni (DeKay)
+
+Figs. 38 and 39
+
+Baculum: Stalk broad, greatest length (3.7 to 4.3 mm.) 1-1/2 times
+greatest breadth, relatively flattened, greatest depth 1/3 greatest
+breadth; single median ossified process, in smaller of two specimens this
+ossification incomplete and of unusual shape (Fig. 39); length of stalk 4
+times length of median process; concavities of basal tuberosities
+medially confluent, constriction less than 1/2 greatest depth; widest
+point of shaft less than 1/4 length of shaft from posteriormost point;
+shaft wider than high except at distal end that is inflated dorsally and
+sometimes laterally; both ventral and dorsal concavities of base of stalk
+broad and moderately deep; posterior profile in dorsal view evenly
+rounded or having marginal notch.
+
+In the absence of ossified lateral processes my two specimens differ from
+bacula of _Microtus (Arvicola) terrestris_ figured by Didier (1943:79,
+1954:245, 247, 248) and by Ognev (1950:591). The median process relative
+to the size of the shaft is smaller, and the shaft relative to its length
+is wider in _M. richardsoni_ than in _M. terrestris_. The stalk of _M.
+(Arvicola) amphibius_ figured by Didier is like that of _M. richardsoni_
+in its greater breadth and median notch on posterior border.
+
+The relationship of the New World water rat, _M. richardsoni_, to the Old
+World water rats (genus _Arvicola_ of some European authors) is
+uncertain. Miller (1896:66) placed all of them in the subgenus
+_Arvicola_. Subsequent authors, stressing differences in the teeth, have
+placed _M. richardsoni_ in the subgenus _Aulacomys_ of Rhoads. Zimmerman
+(1955) has shown that teeth in some _Arvicola_ approach the more complex
+pattern of _M. richardsoni_. He argues also that _Arvicola_ is
+generically distinct from _Microtus_ on the grounds that the two groups
+have separate origins, _Arvicola_ having descended from the genus
+_Mimomys_ and _Microtus_ from some other group of microtines. This
+argument also was advanced by Hinton (1926:47-48). Pending further
+studies of the possible polyphyletic origin of other subgenera of the
+genus _Microtus_, I refer both _M. richardsoni_ and _M. terrestris_ to
+the subgenus _Arvicola_.
+
+The evidence afforded by the bacula available is not conclusive as to
+relations of Old World and New World water rats. No general agreement on
+the number of species in this Palaearctic group has been reached, and
+bacula of only three or four of the numerous Old World subspecies have
+been figured. I have examined none.
+
+_Specimens examined_: Two, from Wyoming; 42454 (31 mi. N Pinedale, 8025
+ft., Sublette Co.), 37903 (23-1/2 mi. S, 5 mi. W Lander, 8600 ft.,
+Fremont Co.).
+
+
+Microtus (Chilotus) oregoni (Bachman)
+
+Fig. 45
+
+Baculum: Stalk broad, greatest length (2.2 mm.) 1-3/4 times greatest
+breadth, 3-1/2 times greatest depth; three well-developed ossified
+processes; median process 2/5 length of stalk, rounded or tapered
+terminally, proximal end opposed to tip of stalk and flattened obliquely;
+lateral processes 2/3 length of median process, deeper than wide, curved;
+tuberosities of stalk well developed, confluent medially, visible in
+dorsal view; in end-view dorsal concavity narrow, moderately deep,
+rounded, ventral concavity wide, deep, flattened; base wider ventrally
+than dorsally; shaft tapering more or less uniformly, terminally
+inflated.
+
+In the relative sizes, to each other and to the stalk, of the three
+digitate ossifications _M. oregoni_ resembles closely the Old World
+representative of the same subgenus, _M. (Chilotus) socialis_, as figured
+by Argyropulo (1933b:181). In _M. oregoni_ the greatest width of the
+baculum is more proximal on the stalk than in the _M. socialis_ figured
+by Argyropulo but closely resembles the baculum of the _M. socialis_
+figured by Didier (1954:242). In possessing a shallow emargination in the
+base of the stalk and in possessing a median process that is smaller than
+the lateral processes, _M. socialis_, as figured by Didier, differs from
+_M. oregoni_. The baculum figured by Argyropulo (_loc. cit._) of
+_Sumeriomys colchicus schidlovskii_ [ = _Microtus (Chilotus) socialis
+schidlovskii_ according to Ognev, 1950:392] differs from other _Chilotus_
+that have been studied in having an unusually elongate median process and
+a more distal placement of the widest part of the stalk.
+
+_Specimens examined_: Three, of the subspecies _M. oregoni oregoni_, from
+5 mi. N Orick, Humboldt Co., California, 3-C-248, collection of W. B.
+Quay; from Mary's Peak, Benton Co., Oregon, 66, collection of F. W.
+Sturges; and from Sec. 3, T. 11S, R. 5W, Benton Co., Oregon, 79183.
+
+
+Microtus (Stenocranius) gregalis (Pallas)
+
+Fig. 34
+
+Baculum: Length of stalk (2.4 mm.) 1-3/4, times greatest breadth, 4-1/3
+times greatest depth; median ossified process well developed, more than
+1/3 length of stalk, higher than wide, slightly bowed, closely appressed
+to terminus of shaft; basal tuberosities of stalk moderately developed,
+confluent medially, posterior profile of medial apex rounded in dorsal
+view, lateral indentations present, hence trilobate outline; in proximal
+end-view base wider ventrally, ventral concavity broader than dorsal
+concavity but of equal depth, medial constriction 2/3 greatest depth;
+shaft slender in distal part, inflated terminally, and wider than high at
+mid-point of stalk; lateral profile a smooth slope of gradually
+decreasing curvature from point of greatest width to near distal end.
+
+The baculum of this species figured by Ognev (1950:461) differs in having
+lateral ossified processes, and a more rounded base of the stalk.
+Resemblance to the New World _Stenocranius_ is discussed below.
+
+_Specimen examined_: One from "Eastern Europe," 8059.
+
+
+Microtus (Stenocranius) miurus Osgood
+
+Figs. 32 and 33
+
+Baculum: Length of stalk (2.8 mm.) 1-1/2 times greatest breadth, 3-1/2
+times greatest depth; median process ossified, 2/5 to 3/5 length of
+stalk, laterally compressed, sometimes arched in dorsoventral plane;
+lateral processes cartilaginous, slender; basal tuberosities well
+developed, averaging less enlarged than shown in Figure 32, but more
+angular in lateral outline than shown in Figure 33; tuberosities
+confluent posteriorly; posterior profile smoothly rounded to trilobate,
+curvature at point of greatest breadth usually acute; in proximal
+end-view base wider dorsally, deep dorsal concavity, shallow ventral
+concavity, medial constriction 3/5 of greatest depth; shaft slender
+anteriorly, at mid-point of stalk twice as wide as high, at tip higher
+than wide, laterally inflated; lateral profile in most specimens abruptly
+curved anterior to point of greatest breadth.
+
+The single specimen of the Old World _M. (Stenocranius) gregalis_
+examined resembles the New World _M. (Stenocranius) miurus_ in the
+angular lateral profile at the point of greatest breadth of the stalk,
+slender shaft in comparison to broad base of stalk, and presence of a
+single well-developed laterally compressed median process. The base of
+the stalk in the baculum of _M. gregalis_ is less well developed and
+smaller than in the baculum of _M. miurus_.
+
+_Specimens examined_: Nine, all of the subspecies _Microtus miurus
+muriei_, from the Brooks Range, Alaska; 51077 (Lake Schrader, 145 deg.09'50",
+69 deg.24'28", 2900 ft., Romanzof Mts.); 51151, 51152, 51154, 51164, 51166,
+51169 (last 6 from Wahoo Lake, 69 deg.08', 146 deg.58', 2350 ft.); 51210, 51213
+(last 2 from Porcupine Lake, 68 deg.51'57", 146 deg.29'50", 3140 ft.).
+
+
+Microtus (Chionomys) nivalis Martins
+
+Fig. 47
+
+Baculum: Greatest length of stalk (2.7 mm.) 2-1/4 times greatest breadth,
+4-1/2 times greatest depth; three digitate processes, lateral processes
+mostly cartilaginous in single adult examined; median process well
+ossified, approximately 1/3 length of stalk, basally notched, not arched,
+laterally compressed distally; base of stalk broad and flat, basal
+tuberosities well developed, separate; posterior profile in dorsal view
+rounded, convex except for medial notch separating tuberosities; dorsal
+and ventral concavities deep, broad, equal; medial constriction less than
+1/2 greatest depth; in dorsal view shaft tapering gradually from widest
+point, terminally rounded; at mid-point of stalk almost twice as wide as
+high.
+
+In the elongate, largely cartilaginous lateral processes of the baculum,
+the specimen described above resembles _M. longicaudus_. The size of the
+median process in comparison to the size of the stalk is also the same.
+The lateral processes have larger ossifications and the base of the stalk
+is more robust in _M. longicaudus_ than in _M. nivalis_.
+
+The well ossified lateral processes and enlarged base of Didier's
+(1954:240) specimen suggest that it is of a more mature individual than
+the one described above. These specimens of _M. nivalis_, as well as the
+specimens of _M. longicaudus_, exhibit dorso-ventral flattening of the
+mid-part of the base of the stalk.
+
+The baculum of a specimen from Switzerland is weakly developed, of small
+size (shaft 2.0 mm. in length), slender, thin, spatulate, and terminally
+inflated. Digital processes were not observed, perhaps owing to excessive
+maceration in preparation. The general appearance of the baculum is that
+of an immature individual, although the animal was not small (165 mm.
+total length in preservative).
+
+_Specimens examined_: Two _Microtus nivalis nivalis_; Zermatt, Valais,
+Switzerland, 67105; Wetterstein, Germany, 65127.
+
+
+Microtus (Chionomys) longicaudus (Merriam)
+
+Fig. 48
+
+Baculum: Base of stalk well developed, greatest length (3 mm.) 1-3/4
+times greatest breadth, 3-2/3 times greatest depth; three ossified
+processes; base of median process rounded; median process slightly curved
+in dorsoventral plane, in length almost 1/3 greatest length of stalk;
+ossifications in lateral processes variable in size, frequently widely
+separated from shaft by cartilage, rarely as large as median
+ossification; basal tuberosities usually well-developed, medially
+confluent; profile of base in dorsal view trilobate or irregularly convex
+throughout; constriction 1/2 greatest depth; shaft relatively straight or
+slightly bowed ventrally or dorsally, shaft at mid-point of stalk wider
+than high; tip of shaft laterally inflated; widest point of stalk
+approximately 1/4 length of stalk from proximal end; lateral profile in
+dorsal view tapers gradually onto shaft anteriorly from point of greatest
+width of stalk; shaft variable, from slender terminally and nearly
+parallel sided (Fig. 48), to broad distally and tapered.
+
+In many of the features that distinguish _M. longicaudus_ (and the
+closely related insular species _M. coronarius_) from other North
+American _Microtus_, _longicaudus_ resembles the Old World species of the
+subgenus _Chionomys_ (that is to say, _M. nivalis_, _M. gud_, and _M.
+roberti_). These features are medium size, long tail, grayish color,
+montane habitat, relatively short molar tooth-row, moderate sized and
+unconstricted incisive foramen, relatively decurved upper incisors,
+elongate nasals, relatively broad interorbital region without
+well-developed median ridge, and similar chromosomes (Matthey, 1955:178).
+For these reasons I am here referring _Microtus longicaudus_ to the
+subgenus _Chionomys_; previously it has not been referred to that
+subgenus.
+
+_Specimens examined_: Six, of three subspecies; _Microtus longicaudus
+littoralis_, Sullivan Island, Alaska, 42972, 42969; _M. l. mordax_, 3/4
+mi. N, 2 mi. W Allenspark, 8400 ft., Boulder Co., Colorado, 50335, 76829;
+_M. l. sierrae_, Crane Flat, Mariposa Co., California, 50252, 50253.
+
+
+Microtus arvalis (Pallas)
+
+Fig. 22
+
+Baculum: In the single specimen examined, stalk small, greatest length
+(2.3 mm.) 2-1/3 times greatest width, almost 6 times greatest depth,
+flattened proximally; three well-developed digitate processes, the median
+one ossified, the lateral processes cartilaginous; median ossification
+laterally compressed and decurved at tip, bilobate at base; basal
+tuberosities of stalk weakly developed, medially confluent; posterior
+profile in dorsal view evenly rounded; ventral concavity deeper and
+narrower than dorsal concavity, but both comparatively shallow; medial
+constriction 2/3 greatest depth; shaft straight, at mid-point twice as
+wide as deep; lateral profile tapering from greatest width gradually to
+parallel sides of distal third of stalk.
+
+From the baculum of _Microtus arvalis_ figured by Ognev (1950:173), and
+from the baculum figured by Didier (1954:238) my specimen differs in the
+absence of lateral ossifications in the digitate processes, smaller and
+slenderer median ossification, and weaker base. These differences in part
+may be owing to a difference in age, my specimen being the less mature.
+
+_Specimen examined_: One from Vidy, Switzerland, 67101.
+
+
+Microtus orcadensis Millais
+
+Fig. 24
+
+Baculum: In the one specimen examined, stalk broad, greatest length (2.6
+mm.) 1-1/2 times greatest breadth, 3-1/2 times greatest depth; three
+digitate processes ossified; median process relatively broad, in length
+more than 1/2 length of stalk, triangular in dorsal view, with small
+spurs posterolaterally, middorsal ridge posteriorly; lateral
+ossifications slightly curved, slenderer, less than 1/2 depth and less
+than 1/2 transverse thickness of median process; basal tuberosities
+well-developed, confluent medially; in end-view base wider dorsally than
+ventrally, dorsal concavity broader and more abruptly curved at mid-point
+than ventral concavity; constriction 1/2 greatest depth; posterior
+profile in dorsal view notched, setting off a posterior shelf; stalk
+including shaft wider than deep throughout, at mid-point width twice
+depth; lateral profile abruptly curved anterior to point of greatest
+width, sides of shaft tapering gradually anteriorly to rounded uninflated
+tip.
+
+The baculum of this insular species, placed in the "_arvalis_" group by
+Ellerman (1941:595), resembles the baculum of both _Microtus agrestis_
+and _Microtus guentheri_ more than it resembles the baculum of _Microtus
+arvalis_. Similarities in the chromosomes of _M. arvalis_ and _M.
+orcadensis_ were noted by Matthey (1953:254, 279), who was of the opinion
+that _M. orcadensis_ is an insular derivative of the _arvalis_-group.
+
+_Specimen examined_: One from the Orkney Islands, 67106.
+
+
+Microtus guentheri Danford and Alston
+
+Fig. 23
+
+Baculum: In the one specimen examined, stalk broad, greatest length (2.9
+mm.) 1-1/2 times greatest breadth, 3-1/2 times greatest depth; three
+digitate processes ossified; median process slightly less than 1/2 length
+of stalk, broad, dorsally curved; curved lateral ossifications shorter
+and more slender than median ossification; basal tuberosities well
+developed, angular, confluent across posterior border of projecting
+shelf; in end-view tuberosities projecting ventrolaterally from central
+shelf; dorsal surface at medial constriction flat, ventral surface
+broadly and deeply concave; posterior profile in dorsal view trilobate,
+central lobe formed by posteriorly flattened shelf, surface of attachment
+visible only on lateral lobes; at mid-point stalk almost twice as wide as
+deep, depth of shaft greater than width proximal to inflated terminus.
+
+_Specimen examined_: One from Palestine, 67104.
+
+
+Microtus fortis Buechner
+
+Fig. 25
+
+Baculum: Stalk large, greatest length (3.8 mm.) 1-4/5 times greatest
+breadth, 4-1/2 times greatest depth; three digitate processes ossified;
+median ossification almost 1/3 length of stalk; lateral ossifications
+slender, smaller than median ossification; posterior profile of stalk in
+dorsal view trilobate, basal tuberosities well developed, confluent
+medially; in end-view dorsal concavity broader and deeper than ventral
+concavity; medial constriction pronounced (less than 1/2 greatest depth);
+lateral profile at widest point of stalk convex, becoming abruptly
+concave as the flange of the basal tuberosities grades into the shaft,
+then gradually converging to narrowest point 1/3 of length of stalk from
+the terminus; stalk wider than deep in proximal 2/3, circular in cross
+section in terminal 1/3, slight terminal inflation.
+
+A specimen figured by Ognev (1950:297) has the same general proportions,
+slender lateral processes, and proximal placement of the point of
+greatest breadth.
+
+_Specimens examined_: Two from Chipo-ri, Korea, 60443, 63841.
+
+
+Microtus montanus (Peale)
+
+Figs. 19, 20 and 21
+
+Baculum: Stalk broad, greatest length (varying with subspecies from 2.3
+to 3.1 mm.) 1-1/2 to 1-3/4 times greatest breadth, 3-1/3 to 4-1/3 times
+greatest depth; three ossified processes, median one largest, more than
+twice as wide and as deep as shorter, slenderer, lateral processes;
+median process laterally compressed distally except in one specimen in
+which moderately inflated distally, proximally enlarged in some specimens
+(Fig. 21) and 1/3 to 2/5 length of stalk; base broad, posterior profile
+in dorsal view evenly convex throughout, at widest point of stalk
+abruptly incurved; basal tuberosities moderately to strongly developed,
+medially confluent; in end-view base wider ventrally than dorsally,
+dorsal concavity slightly to much deeper than the nearly flattened
+ventral concavity; medial constriction 2/3 to 4/5 of greatest depth;
+shaft relatively slender, at mid-point of stalk slightly wider than high
+and 1/4 as wide as base of stalk, terminally rounded or slightly
+inflated; lateral profile in dorsal view a gradual curve from point of
+greatest width anteriorly onto shaft.
+
+The different subspecies figured show the essential characteristics of
+the species, differing primarily in size.
+
+_Specimens examined_: Fourteen, of three subspecies; _Microtus montanus
+amosus_, 1/2 mi. E Soldier Summit, Wasatch Co., Utah, 62241; _M. montanus
+fusus_, La Manga Pass, Conejos Co., Colorado, 42164; 5 mi. N, 26 mi. W
+Saguache, 9500 ft., Saguache Co., Colorado, 42307, 42315; 5 mi. N, 27 mi.
+W Saguache, 9350 ft., Saguache Co., Colorado, 42308; 5 mi. N, 28 mi. W
+Saguache, 9325 ft., Saguache Co., Colorado, 42309; 5 mi. S, 24 mi. W
+Antonito, 9600 ft., Conejos Co., Colorado, 42327, 42330; Prater Canyon,
+Mesa Verde National Park, Montezuma Co., Colorado, 69456, 69457, 69463;
+_Microtus montanus nanus_, 2 mi. N, 2 mi. W Pocatello, Bannock Co.,
+Idaho, 57470, 57472; 3/4 mi. N, 2 mi. W Allenspark, 8400 ft., Boulder
+Co., Colorado, 50330.
+
+
+Microtus townsendii (Bachman)
+
+Fig. 41
+
+Baculum: Stalk broad, greatest length (3.0 mm.) 1-1/2 times greatest
+breadth, 4-1/2 times greatest depth; three ossified processes, median one
+largest, deeper and more than twice as wide as curved, shorter,
+compressed lateral processes and more than 2/5 as long as stalk; base
+broad, in dorsal view posterior profile trilobate, basal tuberosities
+visible; basal tuberosities well developed, medially confluent; in
+end-view base wider ventrally than dorsally, dorsal concavity deeper than
+ventral concavity; medial constriction 3/5 of greatest depth; shaft
+broad, at mid-point more than twice as wide as high and 1/3 as wide as
+base of stalk, terminally rounded.
+
+_Specimens examined_: Three, all _M. t. townsendii_; Fort Lewis, Pierce
+Co., Washington, 57998, subadult; Sec. 33, T. 11S, R. 5W, Benton Co.,
+Oregon, 79186; Sec. 5, T. 12S, R. 4W, Benton Co., Oregon, 79188.
+
+
+Microtus oeconomus (Pallas)
+
+Fig. 44
+
+Baculum: Stalk broad and flattened, greatest length (3.5 mm.) 1-2/3 to 2
+times greatest width, 4 to 5-1/2 times greatest depth; three ossified
+processes, median one largest, lateral processes slender, relatively
+small; length of median process 3/8 length of stalk; median process
+decurved, dorsoventrally flattened in some specimens, widened at base;
+attachment of processes to shaft displaced ventrally; base of stalk
+widened, posterior profile in dorsal view usually trilobate, in a few
+cases rounded, median lobe forming posterior shelf, lateral lobes
+dorsally raised and forming margins of lateral tuberosities; in end-view
+thickness frequently more or less uniform throughout central part, broad
+depression dorsally, ventral concavity narrower and shallower (as
+figured); base, and occasionally shaft, flattened, width at mid-point of
+stalk 2 to 3 times depth, narrowest point posterior to terminal inflation
+of shaft in terminal 1/3 of shaft.
+
+The baculum of _M. oeconomus_ (Old World) figured by Ognev (1950:257)
+resembles but exceeds that of _M. oeconomus_ (New World) in the
+relatively large median process and slender lateral processes, but
+differs noticeably in the presence of a deep median notch in the base of
+the stalk. A specimen from Hungary is intermediate between Ognev's
+specimen and those from the New World in both size of median process and
+size of lateral processes, and has an unnotched base resembling that in
+Figure 44.
+
+_Specimens examined_: Ten, of three subspecies; _M. oeconomus gilmorei_,
+Umiat, Alaska, 51354, 51361, 51399, 51408; Lake Schrader, Brooks Range,
+Alaska, 51422; _M. o. macfarlani_, 5 mi. NNE Gulkana, Alaska, 43039,
+43041; 20 mi. NE Anchorage, Alaska, 43044; Kelsall Lake, British
+Columbia, 43048; _M. o. mehelyi_, Kisbalatan, Hungary, 75159.
+
+
+Microtus mexicanus (Saussure)
+
+Figs. 35 and 36
+
+Baculum: Stalk attenuate, greatest breadth relatively near proximal end;
+greatest length (3.1 to 3.4 mm.) more or less twice greatest breadth, 4
+to 5 times greatest depth; usually a single process ossified; lateral
+processes relatively small, cartilaginous or (in three specimens, 63094,
+69453, 68019) with small ossifications; median process relatively small,
+sometimes appressed to tip of shaft, in length less than 1/4 length of
+stalk; posterior profile in dorsal view rounded, flattened posteriorly,
+or in some specimens trilobate with angular edges; in end-view relative
+depths of dorsal and ventral concavities variable, dorsal usually deeper
+than ventral; distal end of stalk frequently bowed dorsally; shaft
+slender distally, sometimes slightly inflated terminally, or (in one
+specimen, 63085) near tip small lateral projections that are perhaps
+fused lateral ossifications; lateral profile in dorsal view a gradual
+slope anteriorly from point of greatest width to slender tip.
+
+_Specimens examined_: Thirteen, of four subspecies; _Microtus mexicanus
+mexicanus_, Las Vigas, Veracruz, 30692; Nevada de Toluca, Mexico, 63101;
+Valle de Bravo, Mexico, 63094; _Microtus mexicanus mogollonensis_, Mt.
+Taylor, Valencia Co., New Mexico, 63298, 76830; Park Well, Mesa Verde
+National Park, Montezuma Co., Colorado, 69448, 69453; Upper Nutria,
+McKinley Co., New Mexico, 69997, 70000; _Microtus mexicanus phaeus_,
+Sierra Patamba, 9000 ft., Michoacan, 63085; _Microtus mexicanus
+subsimus_, 2 mi. E Mesa de Tablas, Coahuila, 58916; 13 mi. E San Antonio
+de las Alazanas, Coahuila, 68019, 68021.
+
+
+Microtus californicus (Peale)
+
+Fig. 37
+
+Baculum: Stalk elongate, greatest length (3.0 mm.) 2-1/3 times greatest
+breadth, 4-1/2 times greatest depth; median process ossified, 1/4 length
+of stalk, basally broadened, flattened and shallowly grooved ventrally to
+fit tip of shaft, to which the process is closely appressed; lateral
+processes cartilaginous; ends of stalk bowed upwardly; posterior profile
+of base of stalk rounded or slightly trilobate if posterolateral
+concavities form in tuberosities; moderate development of tuberosities,
+in end-view dorsal concavity slightly deeper and narrower than ventral
+concavity, both comparatively shallow, median constriction 4/5 greatest
+depth; shaft curved, more or less terete at mid-point of stalk,
+terminally inflated dorsally; lateral profile in dorsal view gradually
+curved from point of greatest width anteriorly onto shaft.
+
+_Specimens examined_: Two, of two subspecies; _Microtus californicus
+californicus_, 1 mi. NE Berkeley, in Contra Costa Co., California, 76828;
+_Microtus californicus mohavensis_, 1/2 mi. SE Victorville, San
+Bernardino Co., California, 63745.
+
+
+Microtus pennsylvanicus (Ord)
+
+Figs. 14, 15, 16 and 17
+
+Baculum: Stalk heavy, broad, greatest length (2.2 to 3.0 mm.) 1-1/3 to
+1-2/3 times greatest breadth, up to 3-3/4 times greatest depth; three
+ossified processes, median one largest, usually not twice so deep as
+lateral ossifications; median process usually distinctly widened basally,
+in length approximately 1/2 length of stalk; base broad, frequently
+angular laterally and basally, sometimes bilobate; basal tuberosities
+well developed, medially confluent; in end-view more or less uniformly
+biconvex or ventral surface more flattened than dorsal surface, medial
+constriction 1/2 to 2/3 greatest depth; shaft relatively heavy, at
+mid-point stalk almost twice as wide as deep and 1/3 as wide as base of
+stalk; shaft terminally rounded and sometimes slightly inflated; lateral
+profile in dorsal view abruptly or gradually curved anterior to point of
+greatest width and then gradually curved anteriorly.
+
+Specimens examined averaged slightly smaller and were more variable than
+those described by Hamilton (1946:382). The greater variation may be in
+part geographic, as five subspecies are represented. Lateral processes
+are the last to ossify. One specimen (75082) with well-ossified median
+process lacks any lateral ossification. Four bacula of _M.
+pennsylvanicus_ (locality not specified) studied by Dearden (1958:547)
+agree in general with the description above.
+
+One specimen shows a break, perhaps resulting from injury, in the shaft
+(Fig. 14). One specimen has a posteromedian spine on the median digital
+ossification (Fig. 16). Comparison with _M. agrestis_ is included with
+the description of _M. agrestis_.
+
+_Specimens examined_: Thirteen, of six subspecies; _Microtus
+pennsylvanicus alcorni_, 20 mi. NE Anchorage, Alaska, 43043; _Microtus
+pennsylvanicus finitus_, Laird, Yuma Co., Colorado, 68544; _Microtus
+pennsylvanicus modestus_, 5 mi. N, 26 mi. W Saguache, 9500 ft., Saguache
+Co., Colorado, 42306; 3 mi. N, 16 mi. W Saguache, 8500 ft., Saguache Co.,
+Colorado, 42416, 42417, 42418; 1 mi. S, 2 mi. E Eagle Nest, 8100 ft.,
+Colfax Co., New Mexico, 42430, 42439; _Microtus pennsylvanicus
+pennsylvanicus_, 2 mi. S, 3 mi. E Ft. Thompson, 1370 ft., Buffalo Co.,
+South Dakota, 42379; Vermillion, Clay Co., South Dakota, 37070; _Microtus
+pennsylvanicus pullatus_, 12 mi. S, 5 mi. E Butte, Silver Bow Co.,
+Montana, 57501, 57503; _Microtus pennsylvanicus uligocola_, Muir Springs,
+2 mi. N, 2-1/2 mi. W Ft. Morgan, Morgan Co., Colorado, 75082.
+
+
+Microtus agrestis (Linnaeus)
+
+Fig. 18
+
+Baculum: Greatest length of stalk (2.9 mm.) twice greatest breadth, 4-1/2
+times greatest depth; stalk well developed, shaft not flattened
+dorsoventrally; large median ossified process, minute lateral
+ossifications in single specimen examined; length of stalk 2-1/2 times
+length of median ossification which is higher than wide, slightly
+decurved, sagittate in dorsal view, with three-cornered base; basal
+tuberosities of stalk moderately well developed, medially joined;
+posterior profile in dorsal view evenly rounded; ventral concavity
+broader than, but of comparable depth to, dorsal concavity in end-view,
+base of stalk wider ventrally, constriction 3/4 greatest depth; at
+mid-point of stalk shaft is but slightly wider than high; pronounced
+terminal inflation of shaft; lateral profile in dorsal view sloping
+abruptly from widest point of stalk anteriorly onto stalk which then
+tapers more gradually to terminal inflation.
+
+From the baculum of its New World counterpart, namely _Microtus
+pennsylvanicus_, my specimen of _Microtus agrestis_ and the specimen
+figured by Didier (1954:239) differ in their minute lateral processes,
+relatively larger median processes, and more elongate, less
+dorsoventrally flattened shafts.
+
+The specimen of _M. agrestis_ figured by Ognev (1950:320), in dorsal view
+has lateral concavities producing a somewhat trilobate outline in the
+base of the stalk, and the lateral processes are well developed; the
+median process is larger and bulbous, wider distally than proximally.
+Without larger numbers of bacula of _M. agrestis_ I am unable to
+reconcile these differences. The differences between _M. agrestis_ and
+_M. pennsylvanicus_ seem comparable to the differences between some other
+species of _Microtus_.
+
+_Specimen examined_: One, from Gryon, Switzerland, 67102.
+
+
+Microtus (Pedomys) ochrogaster (Wagner)
+
+Fig. 31
+
+Baculum: Stalk broad, greatest length (3.2-4.0 mm.) 1-2/3 to 2 times
+greatest breadth, 2-1/2 to 4 times greatest depth; median process
+ossified, relatively small, less than 3/10 length of stalk; lateral
+processes arising from subterminal part of stalk, cartilaginous or with
+small ossifications; posterior profile in dorsal view broadly rounded or
+slightly angular, widest point of stalk 1/6 to 1/4 the length of stalk
+from base; basal tuberosities well developed and medially confluent, in
+end-view dorsally convex, or at least less deeply concave than ventrally;
+shaft straight, base bent ventrally or more commonly dorsally; at
+mid-point of stalk wider than high, often twice as wide as high; viewed
+from above, lateral profile from point of greatest breadth to middle of
+shaft a gradual sigmoid curve; slight terminal inflation of shaft.
+
+_Specimens examined_: Forty-one, of three subspecies; _Microtus
+ochrogaster haydeni_, Muir Springs, 2 mi. N, 2-1/2 mi. W Ft. Morgan,
+Morgan Co., Colorado, 74995, 74998, 74999, 75002; 1 mi. W Laird, Yuma
+Co., Colorado, 57304, 76833; 2 mi. N, 2 mi. W Haigler, Dundy Co.,
+Nebraska, 75016; 2 mi. S Franklin, Franklin Co., Nebraska, 75043, 75044;
+Atwood, Rawlins Co., Kansas, 75020, 75023, 75025, 75027, 75028; 1 mi. N,
+2 mi. E Oberlin, Decatur Co., Kansas, 75030, 75032, 75034, 75035, 75036;
+1-1/2 mi. N, 1/4 mi. E Norton, Norton Co., Kansas, 68327; 1 mi. SW
+Norton, Norton Co., Kansas, 75037; 2 mi. S, 1 mi. W Norton, Norton Co.,
+Kansas, 75038; _M. ochrogaster ochrogaster_, Rydal, Republic Co., Kansas,
+75047-75053, 75060, 75062, 75063, 75066, 75070, 75071, 75073; 1 mi. N, 1
+mi. W Holton, Jackson Co., Kansas, 75077; 2 mi. W Court House, Lawrence,
+Douglas Co., Kansas, 76832; Univ. Kansas Natural History Reservation,
+Douglas Co., Kansas, 68536; _M. ochrogaster taylori_, Meade County State
+Park, Kansas, 68539, 68542.
+
+
+Microtus (Pitymys) pinetorum (LeConte)
+
+Figs. 27 and 28
+
+Baculum: Stalk broad, greatest length (2.5 to 2.7 mm.) 1-2/3 times
+greatest breadth, 4 times greatest depth; median process ossified, size
+small, 1/5 length of stalk, higher than wide, having small anterodorsal
+prominence in both specimens examined; lateral processes cartilaginous,
+relatively small, displaced posteriorly, attenuate; posterior margin in
+dorsal view broadly rounded, or having blunt median apex, convex
+throughout; basal tuberosities moderately well developed, medially
+confluent, barely visible in dorsal view when mature; in end-view median
+constriction 4/5 greatest depth, ventral concavity deeper than dorsal
+concavity, both comparatively shallow; stalk at mid-point 1-1/2 times as
+wide as deep; shaft relatively slender, bowed dorsally at tip, relatively
+straight otherwise; lateral profile in dorsal view a gradual concave
+slope from point of greatest width anteriorly to distal part of shaft.
+
+_Specimens examined_: Two, from Douglas Co., Kansas, 76834 (2 mi. N
+Baldwin), 68545 (1 mi. NE Pleasant Grove).
+
+
+Microtus (Pitymys) parvulus (Howell)
+
+Fig. 40
+
+Baculum: Stalk broad, greatest length (2.4 mm. in specimen examined)
+1-3/4 times greatest breadth, 4 times greatest depth; median process
+ossified, size small, less than 1/4 length of stalk, wider than high,
+terminally flattened; lateral processes cartilaginous, relatively small,
+attenuate; posterior margin in dorsal view flattened, irregularly curved
+with concavities medially and laterally; basal tuberosities well
+developed, medially confluent; visible in dorsal view; in end-view median
+constriction 2/3 greatest depth, ventral concavity well-formed, no dorsal
+concavity; stalk at mid-point twice as wide as deep; shaft relatively
+slender, bowed dorsally toward tip; in dorsal view lateral profile a
+gradual concave slope from point of greatest width anteriorly to distal
+part of shaft; tip of shaft enlarged.
+
+The baculum of _M. parvulus_ resembles that of _M. pinetorum_ more than
+it resembles the baculum of any other microtine studied, differing
+primarily in smaller size.
+
+_Specimen examined_: One, from 1 mi. W Micanopy, Alachua Co., Florida,
+Univ. Florida No. 1508.
+
+
+Microtus (Pitymys) quasiater (Coues)
+
+Figs. 29 and 30
+
+Baculum: Stalk broad, greatest length (2.6-3.2 mm.) 1-1/3 to 1-2/3 times
+greatest breadth, 3-1/3 to 3-2/3 times greatest depth; median process
+ossified, with ventral depression, process 1/4 to 1/3 length of stalk,
+appressed to tip of shaft, wider than high proximally, relatively broad
+terminally; lateral processes cartilaginous, small, attenuate; posterior
+profile of stalk in dorsal view broadly rounded, bilobate, or trilobate,
+median lobe formed by posterior projection of dorsal shelf between
+enlarged lateral tuberosities that form outer lobes, posterolateral faces
+of these tuberosities visible in dorsal view of stalk; in end-view dorsal
+surface slightly concave, ventral concavity broad and deep, median
+constriction 1/2 greatest depth; shaft flattened except tip that is more
+terete, and bowed dorsally; at mid-point, stalk twice as wide as high;
+shaft relatively slender terminally, narrower than median ossification.
+
+The baculum of _M. quasiater_ is the largest and has the best developed
+base and median process of the three American species of the subgenus
+_Pitymys_. The three species closely resemble each other in basic form.
+
+_Specimens examined_: Five, all from Veracruz; Teocelo, 4500 ft., 30709,
+30711; 4 km. N Tlapacoyan, 1700 ft., 24466; 5 km. N Jalapa, 4500 ft.,
+19869, 19878.
+
+
+Microtus (Pitymys) fatioi (Mottaz)
+
+Fig. 26
+
+The baculum of a single specimen (KU 67103) of _M. fatioi_ from Zermatt,
+Valais, Switzerland, was examined. The baculum is immature, as evidenced
+by its small size, slender stalk and absence of ossified processes,
+therefore no characterization is included.
+
+The baculum of another Old World species of the subgenus _Pitymys_, _M.
+pyrenaicus_ from France, figured and described by Didier (1954:242-243),
+differs from all New World _Pitymys_ examined in processing ossified
+lateral processes.
+
+The status of _Pitymys_, as a genus or as a subgenus, is uncertain. Hall
+and Cockrum (1953:448) considered the North American _Pitymys_ and
+_Pedomys_ as subgenera of _Microtus_. They did not state specifically the
+basis for this point of view, but mention the fact that these two
+subgenera (_Pitymys_ and _Pedomys_) closely resemble each other
+cranially. These authors did not study nor comment upon the status of the
+Old World _Pitymys_. It may be asked whether the Old World and New World
+_Pitymys_ have developed as fossorial _Microtus_ independently, or from
+an ancestor common to both groups and not common to any other _Microtus_.
+Matthey (1955:202) found 62 chromosomes (2N) in both the New World
+_Pitymys pinetorum_ and the Old World _Pitymys duodecimcostatus_. This
+suggests, but does not prove, common ancestry.
+
+
+Neofiber alleni True
+
+Fig. 49
+
+Baculum: Stalk massive, greatest length (4.7 mm.) 1-3/4 times greatest
+breadth, 4 times greatest depth; ossification in digitate processes
+variable; in one (KU 27123) of two specimens examined lateral processes
+ossified and median process unossified, as in two specimens examined by
+Hamilton (1946:379) from "southern Florida"; in my other specimen (KU
+27268) that is possibly more mature, median process ossified although
+less deeply stained than lateral ossifications or stalk; posterior
+profile in probable dorsal view roughly rounded; in end-view probable
+dorsal concavity deep, ventral concavity broad but shallow, and with
+center convex; median constriction 3/5 greatest depth; shaft heavy, least
+depth 2/3 greatest depth of base; stalk, at mid-point, slightly wider
+than deep and more than 1/3 width of base; lateral profile in dorsal view
+sharply incurved distal to point of greatest breadth, shaft therefore
+relatively distinct from basal part of stalk; slight subterminal
+constriction; tip less reduced in the two specimens examined than in two
+figured by Hamilton. In preparation, the tissues that make it possible to
+distinguish with certainty the dorsal and ventral surfaces of the baculum
+were removed in both specimens.
+
+_Specimens examined_: Two, of the subspecies _Neofiber alleni alleni_, 2
+mi. S Gainesville, Alachua Co., Florida, 27268; 1 mi. E Courtenay,
+Merritt Island, Brevard Co., Florida, 27123.
+
+
+Lagurus curtatus (Cope)
+
+Fig. 46
+
+Baculum: Stalk slender, greatest length (2.5 mm.) 2 to 2-2/3 times
+greatest breadth, 4 to 5 times greatest depth; three ossified processes;
+median one more than 1/3 length of stalk, curved dorsally toward tip,
+proximally flattened and having acute lateral angles in dorsal view,
+wider than deep except in distal half; lateral processes smaller than
+median one, slenderer, shorter, of approximately same depth, also curved
+dorsally; base of stalk well developed, basal tuberosities medially
+confluent, in part visible in dorsal view, in end-view wider ventrally
+than dorsally, dorsal and ventral concavities of equal depth and both
+wide, medial constriction 1/2 greatest depth; posterior profile in dorsal
+view broadly bilobate; lateral profile with abrupt transition from basal
+tuberosities to gradually converging, slightly curved sides of shaft;
+shaft terminally inflated.
+
+Dearden (1958:543) described and figured the bacula of six subspecies of
+_Lagurus curtatus_ and two Asiatic species, _Lagurus lagurus_ and
+_Lagurus luteus_. He examined at least 34 specimens of _L. curtatus_ and
+found geographic variation in size, breadth of shaft distally, and
+proportions of digital ossifications to each other and to the stalk. The
+description that I have given above pertains to _L. c. levidensis_.
+
+The baculum of the Asiatic _Lagurus (Lagurus) lagurus_ figured by Ognev
+(1950:554) agrees with that of _Lagurus (Lemmiscus) curtatus_, described
+here, in the relatively elongate shaft and slender stalk, the proportions
+of the processes, and the well-formed and moderately enlarged base of the
+stalk. The bacula of three _Lagurus lagurus_ examined by Dearden
+(1958:545) were of older individuals than the specimen that Ognev figures
+and differ from it and from bacula of _Lagurus curtatus_ (all subspecies)
+in the unusual, almost heart shaped, median process, and in larger size.
+_Lagurus luteus_ examined by Dearden (1958:545) differs from both
+_Lagurus lagurus_ and _Lagurus curtatus_ in lacking lateral digital
+ossifications and in having shorter median digital ossifications and
+wider base of stalk.
+
+_Specimens examined_: Seven _Lagurus curtatus levidensis_ from Wyoming; 9
+mi. S Robertson, Uinta Co., 26045, 26053; 8 mi. S, 2-1/2 mi. E Robertson,
+Uinta Co., 26049; Farson, Sweetwater Co., 37906; 16 mi. S, 11 mi. W
+Waltman, Natrona Co., 42457; 32 mi. S, 22 mi. E Rock Springs, 42465,
+42466.
+
+The following key to the bacula in some adult North American Microtinae
+is intended to help point out some of the most important differences. It
+should be noted that not all species can be keyed out on the basis of the
+baculum. The most difficult group in this respect includes the species of
+_Microtus_ that have small or no ossified lateral processes, especially
+species of the subgenera _Pedomys_ and _Pitymys_, and the two species
+_Microtus californicus_ and _Microtus mexicanus_ of the subgenus
+_Microtus_. Another complicating factor is the variability of bacula
+evident in some species even in the small samples available. It is to be
+expected that additional specimens will show variations not yet observed.
+
+
+KEY TO THE BACULA OF SOME NORTH AMERICAN MICROTINES
+
+  1. Length of lateral digital ossifications more than 1/3 breadth
+  of stalk                                                              2
+
+  1'. Length of lateral digital ossifications less than 1/3 breadth
+   of stalk or absent                                                  15
+
+  2. Size small (total length of baculum less than 5.5 mm.)             3
+
+  2'. Size large (total length of baculum more than 5.5 mm.)           14
+
+  3. Width at mid-point of stalk more than 1/3 greatest breadth of
+  stalk                                                                 4
+
+  3'. Width at mid-point of stalk less than 1/3 greatest breadth of
+  stalk,                                                                8
+
+  4. Stalk, viewed from proximal end hour-glass shaped, and width
+  of stalk less than 1/2 length of stalk.... _Phenacomys
+  intermedius_,                                                    p. 197
+
+  4'. Stalk not both hour-glass shaped when viewed from proximal
+  end, and with width less than 1/2 length of stalk                     5
+
+  5. Shaft thin basally, thickness less than 1/3 of greatest breadth    6
+
+  5'. Shaft thick basally, thickness 1/3 or more of greatest breadth    7
+
+  6. Stalk more or less straight, base not deflected. _Microtus
+  oeconomus_,                                                      p. 204
+
+  6'. Stalk spatulate, and base deflected from axis of shaft....
+  _Microtus guatemalensis_,                                        p. 198
+
+  7. Base enlarged, depth nearly 1/2 of breadth.... _Lemmus
+  trimucronatus_,                                                  p. 193
+
+  7'. Base moderately enlarged, depth near 1/3 of breadth....
+  _Microtus pennsylvanicus_, p. 206, or _Microtus townsendii_,     p. 204
+
+  8. Base hour-glass shaped as viewed from proximal end....
+  _Phenacomys intermedius_,                                        p. 197
+
+  8'. Not so                                                            9
+
+  9. Lateral processes separated from tip of shaft by more than the
+  thickness of the lateral process                                     10
+
+  9'. Lateral processes separated from tip of shaft by less than the
+  thickness of the lateral process                                     11
+
+  10. Lateral processes more than 1/2 the width of median
+  process.... _Microtus longicaudus_,                              p. 201
+
+  10'. Lateral processes slender, less than 1/2 the width of median
+  process.... _Microtus montanus_,                                 p. 204
+
+  11. Lateral ossifications equal in length to median
+  ossification.... _Clethrionomys_,                                p. 194
+
+  11'. Lateral ossifications shorter than median ossification          12
+
+  12. Size small, less than 3.4 mm. in total length....
+  _Microtus oregoni_,                                              p. 199
+
+  12'. Size medium, more than 3.4 mm. in total length                  13
+
+  13. Greatest width of stalk at a point about 1/3 of length of
+  stalk from base.... _Microtus chrotorrhinus_ (Hamilton, 1946:382).
+
+  13'. Greatest width of stalk at a point less than 1/3 of length of
+  stalk from base.... _Lagurus curtatus_,                          p. 210
+
+  14. Size of baculum larger, base more than 3 mm. wide, processes
+  all well developed.... _Ondatra zibethicus_,                     p. 198
+
+  14'. Size of baculum smaller, base less than 3 mm. wide, processes
+  poorly developed in some animals.... _Neofiber alleni_,          p. 209
+
+  15. At least one digital ossification present                        16
+
+  15'. Digital ossifications not present.... _Dicrostonyx
+  groenlandicus_,                                                  p. 193
+
+  16. Breadth of stalk at least 1/2 length of stalk                    17
+
+  16'. Breadth of stalk less than 1/2 length of stalk                  19
+
+  17. Length of stalk greater than 3.6 mm. and less than 1-1/2
+  times its greatest breadth.... _Microtus richardsoni_,           p. 199
+
+  17'. Length of stalk usually less than 3.6 mm., or if more than
+  3.6 mm. (up to 4.0 mm.) then length 1-1/2 times or more its
+  greatest breadth                                                     18
+
+  18. Median process attenuate distally in dorsal view, and
+  relatively long (more than twice its own breadth), 1/5 to 3/5 the
+  length of stalk; breadth of stalk usually 2/3 or more length of
+  stalk.... _Microtus miurus_,                                     p. 200
+
+  18'. Median process relatively blunt distally in dorsal view,
+  relatively short (usually less than 1/4 length of stalk), breadth
+  of stalk usually less than 2/3 length of stalk....
+  _Pitymys_, p. 208, _Pedomys_, p. 207, or _Microtus mexicanus_,   p. 205
+
+  19. Distal processes small and firmly ankylosed to distal end of
+  shaft.... _Phenacomys longicaudus_,                              p. 197
+
+  19'. Distal processes if present not firmly ankylosed to distal
+  end of shaft                                                         20
+
+  20. Dorsal concavity of base as viewed from proximal end usually
+  deeper than ventral concavity.... _Microtus mexicanus_,          p. 205
+
+  20'. Dorsal and ventral concavities of base equal in depth or
+  ventral one the deeper                                               21
+
+  21. Total length of baculum more than 3.6 mm.... _Microtus
+  californicus_,                                                   p. 205
+
+  21'. Total length of baculum less than 3.6 mm.... _Synaptomys
+  cooperi_,                                                        p. 194
+
+
+
+
+DISCUSSION
+
+
+Owing to shortness of lower incisors and present geographic distribution
+of the species, Hinton (1926:35) considered the Tribe Lemmi (lemmings) to
+be more primitive than the Tribe Microti (voles). The surviving lemmings
+are specialized in many features and therefore are considered as advanced
+end-products of an evolutionary radiation of a primitive microtine stock,
+of which all earlier stages are extinct.
+
+Hinton regarded _Dicrostonyx_ as the most primitive of the genera of
+lemmings on account of its more complex molar teeth (complexity was
+considered to be primitive), and on account of the presence of three
+primitive longitudinal rows of tubercles in unworn molars. The other
+three genera were arranged in order of increasing specialization as
+follows: _Synaptomys_, _Myopus_, _Lemmus_.
+
+If the baculum tended to retain its primitive character while
+specializations in the external anatomy developed, and if the above
+arrangement is correct the most primitive bacula would be found in
+_Dicrostonyx_ and in _Synaptomys_. The baculum in these two genera in
+comparison to that in _Myopus_ (as figured by Ognev, 1948:512) and
+_Lemmus_ has a slenderer stalk and smaller digital ossifications or none
+at all. The baculum in the genera of lemmings increases in robustness and
+the development of processes from _Dicrostonyx_, to _Synaptomys_, to
+_Myopus_, to _Lemmus_--the same order outlined above for total of
+specialization. The two extremes in this series are near the extremes of
+variation in bacula to be found in all microtines. The baculum in
+lemmings as a group cannot then be considered more primitive than in
+voles as a group, although the voles are usually considered to be more
+advanced. The situation in the voles, as we shall see, casts a different
+light on the matter.
+
+The voles, Tribe Microti, were considered by Hinton (1926:40) to be more
+advanced than the lemmings because the incisors of the voles are longer
+and the root of their last lower molar is lingual to the root of the
+incisor. Hinton thought also that the murine ancestors of microtines had
+shorter incisors and that the backward extension of the incisors in the
+voles is a more ancient feature than the hypsodonty of the molars. A
+trend in the molar teeth has been toward greater hypsodonty. The voles in
+which the molars are least hypsodont are thus considered primitive. These
+include the living genera _Clethrionomys_, _Phenacomys_, _Ondatra_,
+_Dolomys_, _Ellobius_, and _Prometheomys_. Therefore, the baculum, in
+these assumedly primitive genera, would be expected to resemble the
+baculum in the lemmings or at least the most primitive lemmings. This is
+not the case.
+
+The bacula that I have examined of _Clethrionomys_ and _Phenacomys_ have
+well-developed digital ossifications. In this they resemble the baculum
+of the genus _Lemmus_, the most advanced genus of lemmings according to
+Hinton. The baculum of _Dolomys_ has not been studied. The baculum in
+_Ondatra_, and in _Prometheomys_ as illustrated by Ognev (1948:552), also
+possesses well-developed processes. The baculum of _Ellobius_ is small
+and lacks processes (as figured by Ognev, 1950:662). No ossification was
+found in a single specimen of _Ellobius_ examined by me although the
+entire glans penis was removed and cleared without dissection. So far as
+known then, with the exception of _Ellobius_ and _Phenacomys longicaudus_
+(Dearden, 1958:547), the primitive microtines having rooted molars
+possess bacula having three well-developed ossified processes.
+
+Voles of the genus _Microtus_ vary in the structure of the baculum almost
+as much as do the lemmings. Within the single subgenus _Microtus_ some
+individuals of _Microtus mexicanus_, for example, have minute ossified
+lateral processes and other individuals lack these processes; _Microtus
+pennsylvanicus_ and some other species have proportionately large lateral
+ossifications. If the well-developed condition of the baculum in the
+microtines having rooted molars is primitive, then within the genus
+_Microtus_ those species having well-developed bacula may be considered
+primitive.
+
+The genera _Lagurus_ and _Neofiber_ have moderately developed or
+well-developed lateral processes. _Neofiber_ exhibits a tendency, not
+prominent elsewhere, to have a proportionately smaller median process
+rather than reduced lateral processes.
+
+American species of _Microtus_ (genus and subgenus) that have moderately-
+to well-developed ossified lateral processes are _M. townsendii_, _M.
+oeconomus_, _M. pennsylvanicus_, _M. montanus_, and _M. chrotorrhinus_.
+_Microtus_ of other subgenera having this type of baculum include _M.
+(Herpetomys) guatemalensis_, _M. (Chilotus) oregoni_, and _M. (Chionomys)
+longicaudus_.
+
+American species of _Microtus_ (genus and subgenus) in which the lateral
+ossifications are weakly developed or absent (although cartilaginous
+lateral processes are present) include _M. mexicanus_ and _M.
+californicus_. In other subgenera, species of _Microtus_ having reduced
+lateral ossifications are _M. (Pedomys) ochrogaster_, _M. (Pitymys)
+pinetorum_, _M. (Pitymys) parvulus_, _M. (Pitymys) quasiater_, _M.
+(Arvicola) richardsoni_, and _M. (Stenocranius) miurus_.
+
+The microtines are essentially holarctic in distribution. Both of the
+tribes, the lemmings and the voles, as well as primitive representatives
+of each tribe (not considering _Ellobius_) occur in both the Old World
+and New World. It is not certain on which continent (or continents) the
+Microtinae first differentiated. It is certain, however, that at various
+times, both early and late in the evolution of the subfamily,
+representatives have crossed from Eurasia to North America or _vice
+versa_. Each of 10 or more microtines in the New World is more closely
+related to some microtine in the Old World than to any other microtine in
+the New World.
+
+The similarities or differences in the baculum in Old World and New World
+representatives placed in the same genus or subgenus, or thought to be
+"companion species" have been commented upon in accounts of _Lemmus_,
+_Dicrostonyx_, _Clethrionomys_, _Lagurus_, _Arvicola_, _Stenocranius_,
+_Chilotus_, _Chionomys_, _Pitymys_, and in accounts of _Microtus
+agrestis_ as compared with _M. pennsylvanicus_, and _Microtus oeconomus_
+(both Old World and New World).
+
+The baculum in the Microtinae more closely resembles the baculum in the
+Cricetinae of the Old World than in the Murinae, or than in any other
+rodents known to me. This resemblance suggests relationship between
+Microtinae and Cricetinae.
+
+
+
+
+LITERATURE CITED
+
+
+ARGYROPULO, A. I.
+
+  1933a. Die Gattungen und Arten der Hamster (_Cricetinae_ Murray, 1866)
+  der Palaearktik. Zeitschr. f. Saeugetierkunde, 8:129-149, 27 figs. in
+  text.
+
+  1933b. Ueber zwei neue palaearktische Wuehlmaeuse. Zeitschr. f.
+  Saeugetierkunde, 8:180-183, 3 figs. in text.
+
+CALLERY, R.
+
+  1951. Development of the os genitale in the golden hamster,
+  _Mesocricetus (Cricetus) auratus_. Jour. Mamm., 32:204-207, 1 fig. in
+  text.
+
+CHAMBERLAIN, J. L.
+
+  1954. The Block Island meadow mouse, _Microtus provectus_. Jour. Mamm.,
+  35:587-589, 2 tables in text.
+
+DEARDEN, L. C.
+
+  1958. The baculum in _Lagurus_ and related microtines. Jour. Mamm.,
+  39:541-553, 1 fig. in text.
+
+DIDIER, R.
+
+  1943. L'os penien des Campagnols de France du Genre _Arvicola_.
+  Mammalia, 7:74-79, 10 figs. in text.
+
+  1954. Etude systematique de l'os penien des Mammiferes (suite),
+  Rongeurs: Murides. Mammalia, 18:237-256, 14 figs. in text.
+
+ELLERMAN, J. R.
+
+  1941. The families and genera of living rodents. Vol. II. Family
+  Muridae. The British Museum (Natural History), London, pp. xii + 690,
+  50 figs.
+
+FRILEY, CHARLES E.
+
+  1947. Preparation and preservation of the baculum of mammals. Jour.
+  Mamm., 28:395-397, 1 fig. in text.
+
+HALL, E. R., and E. L. COCKRUM.
+
+  1953. A synopsis of the North American microtine rodents. Univ. Kansas
+  Publ., Mus. Nat. Hist., 5:373-498, 149 figs. in text.
+
+HAMILTON, W. J., JR.
+
+  1946. A study of the baculum in some North American Microtinae. Jour.
+  Mamm., 27:378-387, 3 figs. in text.
+
+HIBBARD, C. W., and G. C. RINKER.
+
+  1942. A new bog-lemming (Synaptomys) from Meade County, Kansas. Univ.
+  Kansas Sci. Bull., 28:25-35, 3 figs. in text.
+
+  1943. A new meadow mouse (_Microtus ochrogaster taylori_) from Meade
+  County, Kansas. Univ. Kansas Sci. Bull., 29:255-268, 5 figs. in text.
+
+HINTON, M. A. C.
+
+  1926. Monograph of the voles and lemmings (Microtinae), living and
+  extinct, Vol. I. British Museum (Natural History), London, pp. xvi +
+  488, plus 15 plates, 110 figs. in text.
+
+MATTHEY, R.
+
+  1953. Les Chromosomes des Muridae. Revue Suisse de Zoologie,
+  60:225-283, avec les planches 1 a 4 groupant 84 photomicrographies, 98
+  figures et 5 schemas dans le texte.
+
+  1955. Nouveaux documents sur les chromosomes des Muridae. Problemes de
+  cytologie comparee et de taxonomie chez les Microtinae. Revue Suisse de
+  Zoologie, 62:163-206, avec 114 figures.
+
+MILLER, G. S.
+
+  1896. Genera and subgenera of voles and lemmings. North American Fauna
+  No. 12, pp. 1-85, 40 figs. and 3 plates in text.
+
+OGNEV, S. I.
+
+  1948. The mammals of Russia (USSR) and adjacent countries (The mammals
+  of Eastern Europe and Northern Asia), Vol. 6. Publ. Acad. Sci. USSR,
+  pp. 1-587, 260 figs., 12 maps, and 11 color plates in text (in
+  Russian).
+
+  1950. The mammals of Russia (USSR) and adjacent countries (The mammals
+  of Eastern Europe and Northern Asia), Vol. 7. Publ. Acad. Sci. USSR,
+  pp. 1-736, 347 figs., 15 maps, and 10 color plates in text (in
+  Russian).
+
+RUTH, E. B.
+
+  1934. The os priapi: A study in bone development. Anat. Rec.,
+  60:231-249, 16 figs. in 3 plates.
+
+SMITH, D. A., and J. B. FOSTER.
+
+  1957. Notes on the small mammals of Churchill, Manitoba. Jour. Mamm.,
+  38:98-115, 3 figs. and 3 tables in text.
+
+WHEELER, B.
+
+  1956. Comparison of the Block Island "species" of _Microtus_ with _M.
+  pennsylvanicus_. Evolution, 10:176-186, 4 figs. and 2 tables in text.
+
+WHITE, J. A.
+
+  1951. A practical method for mounting the bacula of small mammals.
+  Jour. Mamm., 32:125.
+
+ZIMMERMAN, K.
+
+  1955. Die Gattung _Arvicola_ Lac. im System der Microtinae.
+  Saeugetierkundliche Mitteilungen, 3:110-112, 2 figs. in text.
+
+  _Transmitted August 14, 1959._
+
+28-774
+
+
+
+
+  UNIVERSITY OF KANSAS PUBLICATIONS
+  MUSEUM OF NATURAL HISTORY
+
+
+Institutional libraries interested in publications exchange may obtain
+this series by addressing the Exchange Librarian, University of Kansas
+Library, Lawrence, Kansas. Copies for individuals, persons working in a
+particular field of study, may be obtained by addressing instead the
+Museum of Natural History, University of Kansas, Lawrence, Kansas. There
+is no provision for sale of this series by the University Library which
+meets institutional requests, or by the Museum of Natural History which
+meets the requests of individuals. However, when individuals request
+copies from the Museum, 25 cents should be included, for each separate
+number that is 100 pages or more in length, for the purpose of defraying
+the costs of wrapping and mailing.
+
+* An asterisk designates those numbers of which the Museum's supply (not
+the Library's supply) is exhausted. Numbers published to date, in this
+series, are as follows:
+
+  Vol. 1.  Nos. 1-26 and index. Pp. 1-638, 1946-1950.
+
+  *Vol. 2. (Complete) Mammals of Washington. By Walter W. Dalquest. Pp.
+           1-444, 140 figures in text. April 9, 1948.
+
+  Vol. 3.  *1. The avifauna of Micronesia, its origin, evolution, and
+           distribution. By Rollin H. Baker. Pp. 1-359, 16 figures in
+           text. June 12, 1951.
+
+           *2. A quantitative study of the nocturnal migration of birds.
+           By George H. Lowery, Jr. Pp. 361-472, 47 figures in text. June
+           29, 1951.
+
+           3. Phylogeny of the waxwings and allied birds. By M. Dale
+           Arvey. Pp. 473-530, 49 figures in text, 13 tables. October 10,
+           1951.
+
+           4. Birds from the state of Veracruz, Mexico. By George H.
+           Lowery, Jr., and Walter W. Dalquest. Pp. 531-649, 7 figures in
+           text, 2 tables. October 10, 1951.
+
+Index. Pp. 651-681.
+
+  *Vol. 4. (Complete) American weasels. By E. Raymond Hall. Pp. 1-466, 41
+           plates, 31 figures in text. December 27, 1951.
+
+  Vol. 5.  Nos. 1-37 and index. Pp. 1-676, 1951-1953.
+
+  *Vol. 6. (Complete) Mammals of Utah, _taxonomy_ and _distribution_. By
+           Stephen D. Durrant. Pp. 1-549, 91 figures in text, 30 tables.
+           August 10, 1952.
+
+  Vol. 7.  *1. Mammals of Kansas. By E. Lendell Cockrum. Pp. 1-303, 73
+           figures in text, 37 tables. August 25, 1952.
+
+           2. Ecology of the opossum on a natural area in northeastern
+           Kansas. By Henry S. Fitch and Lewis L. Sandidge. Pp. 305-338,
+           5 figures in text. August 24, 1953.
+
+           3. The silky pocket mice (Perognathus flavus) of Mexico. By
+           Rollin H. Baker. Pp. 339-347, 1 figure in text. February 15,
+           1954.
+
+           4. North American jumping mice (Genus Zapus). By Phillip H.
+           Krutzsch. Pp. 349-472, 47 figures in text, 4 tables. April 21,
+           1954.
+
+           5. Mammals from Southeastern Alaska. By Rollin H. Baker and
+           James S. Findley. Pp. 473-477. April 21, 1954.
+
+           6. Distribution of Some Nebraskan Mammals. By J. Knox Jones,
+           Jr. Pp. 479-487. April 21, 1954.
+
+           7. Subspeciation in the montane meadow mouse, Microtus
+           montanus, in Wyoming and Colorado. By Sydney Anderson. Pp.
+           489-506, 2 figures in text. July 23, 1954.
+
+           8. A new subspecies of bat (Myotis velifer) from southeastern
+           California and Arizona. By Terry A. Vaughan. Pp. 507-512. July
+           23, 1954.
+
+           9. Mammals of the San Gabriel mountains of California. By
+           Terry A. Vaughan. Pp. 513-582, 1 figure in text, 12 tables.
+           November 15, 1954.
+
+           10. A new bat (Genus Pipistrellus) from northeastern Mexico.
+           By Rollin H. Baker. Pp. 583-586. November 15, 1954.
+
+           11. A new subspecies of pocket mouse from Kansas. By E.
+           Raymond Hall. Pp. 587-590. November 15, 1954.
+
+           12. Geographic variation in the pocket gopher, Cratogeomys
+           castanops, in Coahuila, Mexico. By Robert J. Russell and
+           Rollin H. Baker. Pp. 591-608. March 15, 1955.
+
+           13. A new cottontail (Sylvilagus floridanus) from
+           northeastern Mexico. By Rollin H. Baker. Pp. 609-612. April 8,
+           1955.
+
+           14. Taxonomy and distribution of some American shrews. By
+           James S. Findley. Pp. 613-618. June 10, 1955.
+
+           15. The pigmy woodrat, Neotoma goldmani, its distribution and
+           systematic position. By Dennis G. Rainey and Rollin H. Baker.
+           Pp. 619-624, 2 figures in text. June 10, 1955.
+
+Index. Pp. 625-651.
+
+  Vol. 8.  1. Life history and ecology of the five-lined skink, Eumeces
+           fasciatus. By Henry S. Fitch. Pp. 1-156, 26 figures in text.
+           September 1, 1954.
+
+           2. Myology and serology of the Avian Family Fringillidae, a
+           taxonomic study. By William B. Stallcup. Pp. 157-211, 23
+           figures in text, 4 tables. November 15, 1954.
+
+           3. An ecological study of the collared lizard (Crotaphytus
+           collaris). By Henry S. Fitch. Pp. 213-274, 10 figures in text.
+           February 10, 1956.
+
+           4. A field study of the Kansas ant-eating frog, Gastrophryne
+           olivacea. By Henry S. Fitch. Pp. 275-306, 9 figures in text.
+           February 10, 1956.
+
+           5. Check-list of the birds of Kansas. By Harrison B. Tordoff.
+           Pp. 307-359, 1 figure in text. March 10, 1956.
+
+           6. A population study of the prairie vole (Microtus
+           ochrogaster) in northeastern Kansas. By Edwin P. Martin. Pp.
+           361-416, 19 figures in text. April 2, 1956.
+
+           7. Temperature responses in free-living amphibians and
+           reptiles of northeastern Kansas. By Henry S. Fitch. Pp.
+           417-476, 10 figures in text, 6 tables. June 1, 1956.
+
+           8. Food of the crow, Corvus brachyrhynchos Brehm, in
+           south-central Kansas. By Dwight Platt. Pp. 477-498, 4 tables.
+           June 8, 1956.
+
+           9. Ecological observations on the woodrat Neotoma floridana.
+           By Henry S. Fitch and Dennis G. Rainey. Pp. 499-533, 3 figures
+           in text. June 12, 1956.
+
+           10. Eastern woodrat, Neotoma floridana; Life history and
+           ecology. By Dennis G. Rainey. Pp. 535-646, 12 plates, 13
+           figures in text. August 15, 1956.
+
+Index. Pp. 647-675.
+
+  Vol. 9.  1. Speciation of the wandering shrew. By James S. Findley. Pp.
+           1-68, 18 figures in text. December 10, 1955.
+
+           2. Additional records and extension of ranges of mammals from
+           Utah. By Stephen D. Durrant, M. Raymond Lee, and Richard M.
+           Hansen. Pp. 69-80. December 10, 1955.
+
+           3. A new long-eared myotis (Myotis evotis) from northeastern
+           Mexico. By Rollin H. Baker and Howard J. Stains. Pp. 81-84.
+           December 10, 1955.
+
+           4. Subspeciation in the meadow mouse, Microtus
+           pennsylvanicus, in Wyoming. By Sydney Anderson. Pp. 85-104, 2
+           figures in text. May 10, 1956.
+
+           5. The condylarth genus Ellipsodon. By Robert W. Wilson. Pp.
+           105-116, 6 figures in text. May 19, 1956.
+
+           6. Additional remains of the multituberculate genus
+           Eucosmodon. By Robert W. Wilson. Pp. 117-123, 10 figures in
+           text. May 19, 1956.
+
+           7. Mammals of Coahuila, Mexico. By Rollin H. Baker. Pp.
+           125-335, 75 figures in text. June 15, 1956.
+
+           8. Comments on the taxonomic status of Apodemus peninsulae,
+           with description of a new subspecies from North China. By J.
+           Knox Jones, Jr. Pp. 337-346, 1 figure in text, 1 table. August
+           15, 1956.
+
+           9. Extensions of known ranges of Mexican bats. By Sydney
+           Anderson. Pp. 347-351. August 15, 1956.
+
+           10. A new bat (Genus Leptonycteris) from Coahuila. By Howard
+           J. Stains. Pp. 353-356. January 21, 1957.
+
+           11. A new species of pocket gopher (Genus Pappogeomys) from
+           Jalisco, Mexico. By Robert J. Russell. Pp. 357-361. January
+           21, 1957.
+
+           12. Geographic variation in the pocket gopher, Thomomys
+           bottae, in Colorado. By Phillip M. Youngman. Pp. 363-387, 7
+           figures in text. February 21, 1958.
+
+           13. New bog lemming (genus Synaptomys) from Nebraska. By J.
+           Knox Jones, Jr. Pp. 385-388. May 12, 1958.
+
+           14. Pleistocene bats from San Josecito Cave, Nuevo Leon,
+           Mexico. By J. Knox Jones, Jr. Pp. 389-396. December 19, 1958.
+
+           15. New subspecies of the rodent Baiomys from Central
+           America. By Robert L. Packard. Pp. 397-404. December 19, 1958.
+
+           16. Mammals of the Grand Mesa, Colorado. By Sydney Anderson.
+           Pp. 405-414, 1 figure in text, May 20, 1959.
+
+           17. Distribution, variation, and relationships of the montane
+           vole, Microtus montanus. By Sydney Anderson. Pp. 415-511, 12
+           figures in text, 2 tables. August 1, 1959.
+
+           18. Conspecificity of two pocket mice, Perognathus goldmani
+           and P. artus. By E. Raymond Hall and Marilyn Bailey Ogilvie.
+           Pp. 513-518, 1 map in text. January 14, 1960.
+
+           19. Records of harvest mice, Reithrodontomys, from Central
+           America, with description of a new subspecies from Nicaragua.
+           By Sydney Anderson and J. Knox Jones, Jr. Pp. 519-529. January
+           14, 1960.
+
+           20. Small carnivores from San Josecito Cave (Pleistocene),
+           Nuevo Leon, Mexico. By E. Raymond Hall. Pp. 531-538, 1 figure
+           in text. January 14, 1960.
+
+           21. Pleistocene pocket gophers from San Josecito Cave, Nuevo
+           Leon, Mexico. By Robert J. Russell. Pp. 539-548, 1 figure in
+           text, January 14, 1960. More numbers will appear in volume 9.
+
+  Vol. 10. 1. Studies of birds killed in nocturnal migration. By Harrison
+           B. Tordoff and Robert M. Mengel. Pp. 1-44, 6 figures in text,
+           2 tables. September 12, 1956.
+
+           2. Comparative breeding behavior of Ammospiza caudacuta and
+           A. maritima. By Glen E. Woolfenden. Pp. 45-75, 6 plates, 1
+           figure. December 20, 1956.
+
+           3. The forest habitat of the University of Kansas Natural
+           History Reservation. By Henry S. Fitch and Ronald R. McGregor.
+           Pp. 77-127, 2 plates, 7 figures in text, 4 tables. December
+           31, 1956.
+
+           4. Aspects of reproduction and development in the prairie
+           vole (Microtus ochrogaster). By Henry S. Fitch. Pp. 129-161, 8
+           figures in text, 4 tables. December 19, 1957.
+
+           5. Birds found on the Arctic slope of northern Alaska. By
+           James W. Bee. Pp. 163-211, plates 9-10, 1 figure in text.
+           March 12, 1958.
+
+           6. The wood rats of Colorado: distribution and ecology. By
+           Robert B. Finley, Jr. Pp. 213-552, 34 plates, 8 figures in
+           text, 35 tables. November 7, 1958.
+
+           7. Home ranges and movements of the eastern cottontail in
+           Kansas. By Donald W. Janes. Pp. 553-572, 4 plates, 3 figures
+           in text. May 4, 1959.
+
+           8. Natural history of the salamander Aneides hardyi. By
+           Richard F. Johnston and Gerhard A. Schad. Pp. 573-585. October
+           8, 1959.
+
+More numbers will appear in volume 10.
+
+  Vol. 11. 1. The systematic status of the colubrid snake, Leptodeira
+           discolor Guenther. By William E. Duellman. Pp. 1-9, 4 figures.
+           July 14, 1958.
+
+           2. Natural history of the six-lined racerunner, Cnemidophorus
+           sexlineatus. By Henry S. Fitch. Pp. 11-62, 9 figures, 9
+           tables. September 19, 1958.
+
+           3. Home ranges, territories, and seasonal movements of
+           vertebrates of the Natural History Reservation. By Henry S.
+           Fitch. Pp. 63-326, 6 plates, 24 figures in text, 3 tables.
+           December 12, 1958.
+
+           4. A new snake of the genus Geophis from Chihuahua, Mexico.
+           By John M. Legler. Pp. 327-334, 2 figures in text. January 28,
+           1959.
+
+           5. A new tortoise, genus Gopherus, from north-central Mexico.
+           By John M. Legler. Pp. 335-343. April 24, 1959.
+
+           6. Fishes of Chautauqua, Cowley and Elk counties, Kansas. By
+           Artie L. Metcalf. Pp. 345-400, 2 plates, 2 figures in text, 10
+           tables. May 6, 1959.
+
+           7. Fishes of the Big Blue River Basin, Kansas. By W. L.
+           Minckley. Pp. 401-442, 2 plates, 4 figures in text, 5 tables.
+           May 8, 1959.
+
+           8. Birds from Coahuila, Mexico. By Emil K. Urban. Pp.
+           443-516. August 1, 1959.
+
+           9. Description of a new softshell turtle from the
+           southeastern United States. By Robert G. Webb. Pp. 517-525, 2
+           plates, 1 figure in text. August 14, 1959.
+
+Another number will appear in volume 11.
+
+  Vol. 12. 1. Functional morphology of three bats: Eumops, Myotis,
+           Macrotus. By Terry A. Vaughan. Pp. 1-153, 4 plates, 24 figures
+           in text. July 8, 1959.
+
+           2. The ancestry of modern Amphibia: a review of the evidence.
+           By Theodore H. Eaton, Jr. Pp. 155-180, 10 figures in text.
+           July 10, 1959.
+
+           3. The baculum in microtine rodents. By Sydney Anderson. Pp.
+           181-216, 49 figures in text. February 19, 1960.
+
+More numbers will appear in volume 12.
+
+
+
+
+
+
+End of the Project Gutenberg EBook of The Baculum in Microtine Rodents, by
+Sydney Anderson
+
+*** END OF THIS PROJECT GUTENBERG EBOOK THE BACULUM IN MICROTINE RODENTS ***
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