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Title: The Baculum in Microtine Rodents

Author: Sydney Anderson

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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 (× 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


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  *Vol. 2. (Complete) Mammals of Washington. By Walter W. Dalquest. Pp.
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           *2. A quantitative study of the nocturnal migration of birds.
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           3. Phylogeny of the waxwings and allied birds. By M. Dale
           Arvey. Pp. 473-530, 49 figures in text, 13 tables. October 10,
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           4. Birds from the state of Veracruz, Mexico. By George H.
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           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.






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