Chapter II: Part 2

_Specimens examined_: Thirteen, of four subspecies; _Microtus mexicanus mexicanus_, Las Vigas, Veracruz, 30692; Nevada de Toluca, Mexico, 63101; Valle de Bravo, Mexico, 63094; _Microtus mexicanus mogollonensis_, Mt. Taylor, Valencia Co., New Mexico, 63298, 76830; Park Well, Mesa Verde National Park, Montezuma Co., Colorado, 69448, 69453; Upper Nutria, McKinley Co., New Mexico, 69997, 70000; _Microtus mexicanus phaeus_, Sierra Patamba, 9000 ft., Michoacan, 63085; _Microtus mexicanus subsimus_, 2 mi. E Mesa de Tablas, Coahuila, 58916; 13 mi. E San Antonio de las Alazanas, Coahuila, 68019, 68021.

Microtus californicus (Peale)

Fig. 37

Baculum: Stalk elongate, greatest length (3.0 mm.) 2-1/3 times greatest breadth, 4-1/2 times greatest depth; median process ossified, 1/4 length of stalk, basally broadened, flattened and shallowly grooved ventrally to fit tip of shaft, to which the process is closely appressed; lateral processes cartilaginous; ends of stalk bowed upwardly; posterior profile of base of stalk rounded or slightly trilobate if posterolateral concavities form in tuberosities; moderate development of tuberosities, in end-view dorsal concavity slightly deeper and narrower than ventral concavity, both comparatively shallow, median constriction 4/5 greatest depth; shaft curved, more or less terete at mid-point of stalk, terminally inflated dorsally; lateral profile in dorsal view gradually curved from point of greatest width anteriorly onto shaft.

_Specimens examined_: Two, of two subspecies; _Microtus californicus californicus_, 1 mi. NE Berkeley, in Contra Costa Co., California, 76828; _Microtus californicus mohavensis_, 1/2 mi. SE Victorville, San Bernardino Co., California, 63745.

Microtus pennsylvanicus (Ord)

Figs. 14, 15, 16 and 17

Baculum: Stalk heavy, broad, greatest length (2.2 to 3.0 mm.) 1-1/3 to 1-2/3 times greatest breadth, up to 3-3/4 times greatest depth; three ossified processes, median one largest, usually not twice so deep as lateral ossifications; median process usually distinctly widened basally, in length approximately 1/2 length of stalk; base broad, frequently angular laterally and basally, sometimes bilobate; basal tuberosities well developed, medially confluent; in end-view more or less uniformly biconvex or ventral surface more flattened than dorsal surface, medial constriction 1/2 to 2/3 greatest depth; shaft relatively heavy, at mid-point stalk almost twice as wide as deep and 1/3 as wide as base of stalk; shaft terminally rounded and sometimes slightly inflated; lateral profile in dorsal view abruptly or gradually curved anterior to point of greatest width and then gradually curved anteriorly.

Specimens examined averaged slightly smaller and were more variable than those described by Hamilton (1946:382). The greater variation may be in part geographic, as five subspecies are represented. Lateral processes are the last to ossify. One specimen (75082) with well-ossified median process lacks any lateral ossification. Four bacula of _M. pennsylvanicus_ (locality not specified) studied by Dearden (1958:547) agree in general with the description above.

One specimen shows a break, perhaps resulting from injury, in the shaft (Fig. 14). One specimen has a posteromedian spine on the median digital ossification (Fig. 16). Comparison with _M. agrestis_ is included with the description of _M. agrestis_.

_Specimens examined_: Thirteen, of six subspecies; _Microtus pennsylvanicus alcorni_, 20 mi. NE Anchorage, Alaska, 43043; _Microtus pennsylvanicus finitus_, Laird, Yuma Co., Colorado, 68544; _Microtus pennsylvanicus modestus_, 5 mi. N, 26 mi. W Saguache, 9500 ft., Saguache Co., Colorado, 42306; 3 mi. N, 16 mi. W Saguache, 8500 ft., Saguache Co., Colorado, 42416, 42417, 42418; 1 mi. S, 2 mi. E Eagle Nest, 8100 ft., Colfax Co., New Mexico, 42430, 42439; _Microtus pennsylvanicus pennsylvanicus_, 2 mi. S, 3 mi. E Ft. Thompson, 1370 ft., Buffalo Co., South Dakota, 42379; Vermillion, Clay Co., South Dakota, 37070; _Microtus pennsylvanicus pullatus_, 12 mi. S, 5 mi. E Butte, Silver Bow Co., Montana, 57501, 57503; _Microtus pennsylvanicus uligocola_, Muir Springs, 2 mi. N, 2-1/2 mi. W Ft. Morgan, Morgan Co., Colorado, 75082.

Microtus agrestis (Linnaeus)

Fig. 18

Baculum: Greatest length of stalk (2.9 mm.) twice greatest breadth, 4-1/2 times greatest depth; stalk well developed, shaft not flattened dorsoventrally; large median ossified process, minute lateral ossifications in single specimen examined; length of stalk 2-1/2 times length of median ossification which is higher than wide, slightly decurved, sagittate in dorsal view, with three-cornered base; basal tuberosities of stalk moderately well developed, medially joined; posterior profile in dorsal view evenly rounded; ventral concavity broader than, but of comparable depth to, dorsal concavity in end-view, base of stalk wider ventrally, constriction 3/4 greatest depth; at mid-point of stalk shaft is but slightly wider than high; pronounced terminal inflation of shaft; lateral profile in dorsal view sloping abruptly from widest point of stalk anteriorly onto stalk which then tapers more gradually to terminal inflation.

From the baculum of its New World counterpart, namely _Microtus pennsylvanicus_, my specimen of _Microtus agrestis_ and the specimen figured by Didier (1954:239) differ in their minute lateral processes, relatively larger median processes, and more elongate, less dorsoventrally flattened shafts.

The specimen of _M. agrestis_ figured by Ognev (1950:320), in dorsal view has lateral concavities producing a somewhat trilobate outline in the base of the stalk, and the lateral processes are well developed; the median process is larger and bulbous, wider distally than proximally. Without larger numbers of bacula of _M. agrestis_ I am unable to reconcile these differences. The differences between _M. agrestis_ and _M. pennsylvanicus_ seem comparable to the differences between some other species of _Microtus_.

_Specimen examined_: One, from Gryon, Switzerland, 67102.

Microtus (Pedomys) ochrogaster (Wagner)

Fig. 31

Baculum: Stalk broad, greatest length (3.2-4.0 mm.) 1-2/3 to 2 times greatest breadth, 2-1/2 to 4 times greatest depth; median process ossified, relatively small, less than 3/10 length of stalk; lateral processes arising from subterminal part of stalk, cartilaginous or with small ossifications; posterior profile in dorsal view broadly rounded or slightly angular, widest point of stalk 1/6 to 1/4 the length of stalk from base; basal tuberosities well developed and medially confluent, in end-view dorsally convex, or at least less deeply concave than ventrally; shaft straight, base bent ventrally or more commonly dorsally; at mid-point of stalk wider than high, often twice as wide as high; viewed from above, lateral profile from point of greatest breadth to middle of shaft a gradual sigmoid curve; slight terminal inflation of shaft.

_Specimens examined_: Forty-one, of three subspecies; _Microtus ochrogaster haydeni_, Muir Springs, 2 mi. N, 2-1/2 mi. W Ft. Morgan, Morgan Co., Colorado, 74995, 74998, 74999, 75002; 1 mi. W Laird, Yuma Co., Colorado, 57304, 76833; 2 mi. N, 2 mi. W Haigler, Dundy Co., Nebraska, 75016; 2 mi. S Franklin, Franklin Co., Nebraska, 75043, 75044; Atwood, Rawlins Co., Kansas, 75020, 75023, 75025, 75027, 75028; 1 mi. N, 2 mi. E Oberlin, Decatur Co., Kansas, 75030, 75032, 75034, 75035, 75036; 1-1/2 mi. N, 1/4 mi. E Norton, Norton Co., Kansas, 68327; 1 mi. SW Norton, Norton Co., Kansas, 75037; 2 mi. S, 1 mi. W Norton, Norton Co., Kansas, 75038; _M. ochrogaster ochrogaster_, Rydal, Republic Co., Kansas, 75047-75053, 75060, 75062, 75063, 75066, 75070, 75071, 75073; 1 mi. N, 1 mi. W Holton, Jackson Co., Kansas, 75077; 2 mi. W Court House, Lawrence, Douglas Co., Kansas, 76832; Univ. Kansas Natural History Reservation, Douglas Co., Kansas, 68536; _M. ochrogaster taylori_, Meade County State Park, Kansas, 68539, 68542.

Microtus (Pitymys) pinetorum (LeConte)

Figs. 27 and 28

Baculum: Stalk broad, greatest length (2.5 to 2.7 mm.) 1-2/3 times greatest breadth, 4 times greatest depth; median process ossified, size small, 1/5 length of stalk, higher than wide, having small anterodorsal prominence in both specimens examined; lateral processes cartilaginous, relatively small, displaced posteriorly, attenuate; posterior margin in dorsal view broadly rounded, or having blunt median apex, convex throughout; basal tuberosities moderately well developed, medially confluent, barely visible in dorsal view when mature; in end-view median constriction 4/5 greatest depth, ventral concavity deeper than dorsal concavity, both comparatively shallow; stalk at mid-point 1-1/2 times as wide as deep; shaft relatively slender, bowed dorsally at tip, relatively straight otherwise; lateral profile in dorsal view a gradual concave slope from point of greatest width anteriorly to distal part of shaft.

_Specimens examined_: Two, from Douglas Co., Kansas, 76834 (2 mi. N Baldwin), 68545 (1 mi. NE Pleasant Grove).

Microtus (Pitymys) parvulus (Howell)

Fig. 40

Baculum: Stalk broad, greatest length (2.4 mm. in specimen examined) 1-3/4 times greatest breadth, 4 times greatest depth; median process ossified, size small, less than 1/4 length of stalk, wider than high, terminally flattened; lateral processes cartilaginous, relatively small, attenuate; posterior margin in dorsal view flattened, irregularly curved with concavities medially and laterally; basal tuberosities well developed, medially confluent; visible in dorsal view; in end-view median constriction 2/3 greatest depth, ventral concavity well-formed, no dorsal concavity; stalk at mid-point twice as wide as deep; shaft relatively slender, bowed dorsally toward tip; in dorsal view lateral profile a gradual concave slope from point of greatest width anteriorly to distal part of shaft; tip of shaft enlarged.

The baculum of _M. parvulus_ resembles that of _M. pinetorum_ more than it resembles the baculum of any other microtine studied, differing primarily in smaller size.

_Specimen examined_: One, from 1 mi. W Micanopy, Alachua Co., Florida, Univ. Florida No. 1508.

Microtus (Pitymys) quasiater (Coues)

Figs. 29 and 30

Baculum: Stalk broad, greatest length (2.6-3.2 mm.) 1-1/3 to 1-2/3 times greatest breadth, 3-1/3 to 3-2/3 times greatest depth; median process ossified, with ventral depression, process 1/4 to 1/3 length of stalk, appressed to tip of shaft, wider than high proximally, relatively broad terminally; lateral processes cartilaginous, small, attenuate; posterior profile of stalk in dorsal view broadly rounded, bilobate, or trilobate, median lobe formed by posterior projection of dorsal shelf between enlarged lateral tuberosities that form outer lobes, posterolateral faces of these tuberosities visible in dorsal view of stalk; in end-view dorsal surface slightly concave, ventral concavity broad and deep, median constriction 1/2 greatest depth; shaft flattened except tip that is more terete, and bowed dorsally; at mid-point, stalk twice as wide as high; shaft relatively slender terminally, narrower than median ossification.

The baculum of _M. quasiater_ is the largest and has the best developed base and median process of the three American species of the subgenus _Pitymys_. The three species closely resemble each other in basic form.

_Specimens examined_: Five, all from Veracruz; Teocelo, 4500 ft., 30709, 30711; 4 km. N Tlapacoyan, 1700 ft., 24466; 5 km. N Jalapa, 4500 ft., 19869, 19878.

Microtus (Pitymys) fatioi (Mottaz)

Fig. 26

The baculum of a single specimen (KU 67103) of _M. fatioi_ from Zermatt, Valais, Switzerland, was examined. The baculum is immature, as evidenced by its small size, slender stalk and absence of ossified processes, therefore no characterization is included.

The baculum of another Old World species of the subgenus _Pitymys_, _M. pyrenaicus_ from France, figured and described by Didier (1954:242-243), differs from all New World _Pitymys_ examined in processing ossified lateral processes.

The status of _Pitymys_, as a genus or as a subgenus, is uncertain. Hall and Cockrum (1953:448) considered the North American _Pitymys_ and _Pedomys_ as subgenera of _Microtus_. They did not state specifically the basis for this point of view, but mention the fact that these two subgenera (_Pitymys_ and _Pedomys_) closely resemble each other cranially. These authors did not study nor comment upon the status of the Old World _Pitymys_. It may be asked whether the Old World and New World _Pitymys_ have developed as fossorial _Microtus_ independently, or from an ancestor common to both groups and not common to any other _Microtus_. Matthey (1955:202) found 62 chromosomes (2N) in both the New World _Pitymys pinetorum_ and the Old World _Pitymys duodecimcostatus_. This suggests, but does not prove, common ancestry.

Neofiber alleni True

Fig. 49

Baculum: Stalk massive, greatest length (4.7 mm.) 1-3/4 times greatest breadth, 4 times greatest depth; ossification in digitate processes variable; in one (KU 27123) of two specimens examined lateral processes ossified and median process unossified, as in two specimens examined by Hamilton (1946:379) from "southern Florida"; in my other specimen (KU 27268) that is possibly more mature, median process ossified although less deeply stained than lateral ossifications or stalk; posterior profile in probable dorsal view roughly rounded; in end-view probable dorsal concavity deep, ventral concavity broad but shallow, and with center convex; median constriction 3/5 greatest depth; shaft heavy, least depth 2/3 greatest depth of base; stalk, at mid-point, slightly wider than deep and more than 1/3 width of base; lateral profile in dorsal view sharply incurved distal to point of greatest breadth, shaft therefore relatively distinct from basal part of stalk; slight subterminal constriction; tip less reduced in the two specimens examined than in two figured by Hamilton. In preparation, the tissues that make it possible to distinguish with certainty the dorsal and ventral surfaces of the baculum were removed in both specimens.

_Specimens examined_: Two, of the subspecies _Neofiber alleni alleni_, 2 mi. S Gainesville, Alachua Co., Florida, 27268; 1 mi. E Courtenay, Merritt Island, Brevard Co., Florida, 27123.

Lagurus curtatus (Cope)

Fig. 46

Baculum: Stalk slender, greatest length (2.5 mm.) 2 to 2-2/3 times greatest breadth, 4 to 5 times greatest depth; three ossified processes; median one more than 1/3 length of stalk, curved dorsally toward tip, proximally flattened and having acute lateral angles in dorsal view, wider than deep except in distal half; lateral processes smaller than median one, slenderer, shorter, of approximately same depth, also curved dorsally; base of stalk well developed, basal tuberosities medially confluent, in part visible in dorsal view, in end-view wider ventrally than dorsally, dorsal and ventral concavities of equal depth and both wide, medial constriction 1/2 greatest depth; posterior profile in dorsal view broadly bilobate; lateral profile with abrupt transition from basal tuberosities to gradually converging, slightly curved sides of shaft; shaft terminally inflated.

Dearden (1958:543) described and figured the bacula of six subspecies of _Lagurus curtatus_ and two Asiatic species, _Lagurus lagurus_ and _Lagurus luteus_. He examined at least 34 specimens of _L. curtatus_ and found geographic variation in size, breadth of shaft distally, and proportions of digital ossifications to each other and to the stalk. The description that I have given above pertains to _L. c. levidensis_.

The baculum of the Asiatic _Lagurus (Lagurus) lagurus_ figured by Ognev (1950:554) agrees with that of _Lagurus (Lemmiscus) curtatus_, described here, in the relatively elongate shaft and slender stalk, the proportions of the processes, and the well-formed and moderately enlarged base of the stalk. The bacula of three _Lagurus lagurus_ examined by Dearden (1958:545) were of older individuals than the specimen that Ognev figures and differ from it and from bacula of _Lagurus curtatus_ (all subspecies) in the unusual, almost heart shaped, median process, and in larger size. _Lagurus luteus_ examined by Dearden (1958:545) differs from both _Lagurus lagurus_ and _Lagurus curtatus_ in lacking lateral digital ossifications and in having shorter median digital ossifications and wider base of stalk.

_Specimens examined_: Seven _Lagurus curtatus levidensis_ from Wyoming; 9 mi. S Robertson, Uinta Co., 26045, 26053; 8 mi. S, 2-1/2 mi. E Robertson, Uinta Co., 26049; Farson, Sweetwater Co., 37906; 16 mi. S, 11 mi. W Waltman, Natrona Co., 42457; 32 mi. S, 22 mi. E Rock Springs, 42465, 42466.

The following key to the bacula in some adult North American Microtinae is intended to help point out some of the most important differences. It should be noted that not all species can be keyed out on the basis of the baculum. The most difficult group in this respect includes the species of _Microtus_ that have small or no ossified lateral processes, especially species of the subgenera _Pedomys_ and _Pitymys_, and the two species _Microtus californicus_ and _Microtus mexicanus_ of the subgenus _Microtus_. Another complicating factor is the variability of bacula evident in some species even in the small samples available. It is to be expected that additional specimens will show variations not yet observed.

KEY TO THE BACULA OF SOME NORTH AMERICAN MICROTINES

1. Length of lateral digital ossifications more than 1/3 breadth
of stalk 2

1'. Length of lateral digital ossifications less than 1/3 breadth
of stalk or absent 15

2. Size small (total length of baculum less than 5.5 mm.) 3

2'. Size large (total length of baculum more than 5.5 mm.) 14

3. Width at mid-point of stalk more than 1/3 greatest breadth of
stalk 4

3'. Width at mid-point of stalk less than 1/3 greatest breadth of
stalk, 8

4. Stalk, viewed from proximal end hour-glass shaped, and width
of stalk less than 1/2 length of stalk.... _Phenacomys
intermedius_, p. 197

4'. Stalk not both hour-glass shaped when viewed from proximal
end, and with width less than 1/2 length of stalk 5

5. Shaft thin basally, thickness less than 1/3 of greatest breadth 6

5'. Shaft thick basally, thickness 1/3 or more of greatest breadth 7

6. Stalk more or less straight, base not deflected. _Microtus
oeconomus_, p. 204

6'. Stalk spatulate, and base deflected from axis of shaft....
_Microtus guatemalensis_, p. 198

7. Base enlarged, depth nearly 1/2 of breadth.... _Lemmus
trimucronatus_, p. 193

7'. Base moderately enlarged, depth near 1/3 of breadth....
_Microtus pennsylvanicus_, p. 206, or _Microtus townsendii_, p. 204

8. Base hour-glass shaped as viewed from proximal end....
_Phenacomys intermedius_, p. 197

8'. Not so 9

9. Lateral processes separated from tip of shaft by more than the
thickness of the lateral process 10

9'. Lateral processes separated from tip of shaft by less than the
thickness of the lateral process 11

10. Lateral processes more than 1/2 the width of median
process.... _Microtus longicaudus_, p. 201

10'. Lateral processes slender, less than 1/2 the width of median
process.... _Microtus montanus_, p. 204

11. Lateral ossifications equal in length to median
ossification.... _Clethrionomys_, p. 194

11'. Lateral ossifications shorter than median ossification 12

12. Size small, less than 3.4 mm. in total length....
_Microtus oregoni_, p. 199

12'. Size medium, more than 3.4 mm. in total length 13

13. Greatest width of stalk at a point about 1/3 of length of
stalk from base.... _Microtus chrotorrhinus_ (Hamilton, 1946:382).

13'. Greatest width of stalk at a point less than 1/3 of length of
stalk from base.... _Lagurus curtatus_, p. 210

14. Size of baculum larger, base more than 3 mm. wide, processes
all well developed.... _Ondatra zibethicus_, p. 198

14'. Size of baculum smaller, base less than 3 mm. wide, processes
poorly developed in some animals.... _Neofiber alleni_, p. 209

15. At least one digital ossification present 16

15'. Digital ossifications not present.... _Dicrostonyx
groenlandicus_, p. 193

16. Breadth of stalk at least 1/2 length of stalk 17

16'. Breadth of stalk less than 1/2 length of stalk 19

17. Length of stalk greater than 3.6 mm. and less than 1-1/2
times its greatest breadth.... _Microtus richardsoni_, p. 199

17'. Length of stalk usually less than 3.6 mm., or if more than
3.6 mm. (up to 4.0 mm.) then length 1-1/2 times or more its
greatest breadth 18

18. Median process attenuate distally in dorsal view, and
relatively long (more than twice its own breadth), 1/5 to 3/5 the
length of stalk; breadth of stalk usually 2/3 or more length of
stalk.... _Microtus miurus_, p. 200

18'. Median process relatively blunt distally in dorsal view,
relatively short (usually less than 1/4 length of stalk), breadth
of stalk usually less than 2/3 length of stalk....
_Pitymys_, p. 208, _Pedomys_, p. 207, or _Microtus mexicanus_, p. 205

19. Distal processes small and firmly ankylosed to distal end of
shaft.... _Phenacomys longicaudus_, p. 197

19'. Distal processes if present not firmly ankylosed to distal
end of shaft 20

20. Dorsal concavity of base as viewed from proximal end usually
deeper than ventral concavity.... _Microtus mexicanus_, p. 205

20'. Dorsal and ventral concavities of base equal in depth or
ventral one the deeper 21

21. Total length of baculum more than 3.6 mm.... _Microtus
californicus_, p. 205

21'. Total length of baculum less than 3.6 mm.... _Synaptomys
cooperi_, p. 194

DISCUSSION

Owing to shortness of lower incisors and present geographic distribution of the species, Hinton (1926:35) considered the Tribe Lemmi (lemmings) to be more primitive than the Tribe Microti (voles). The surviving lemmings are specialized in many features and therefore are considered as advanced end-products of an evolutionary radiation of a primitive microtine stock, of which all earlier stages are extinct.

Hinton regarded _Dicrostonyx_ as the most primitive of the genera of lemmings on account of its more complex molar teeth (complexity was considered to be primitive), and on account of the presence of three primitive longitudinal rows of tubercles in unworn molars. The other three genera were arranged in order of increasing specialization as follows: _Synaptomys_, _Myopus_, _Lemmus_.

If the baculum tended to retain its primitive character while specializations in the external anatomy developed, and if the above arrangement is correct the most primitive bacula would be found in _Dicrostonyx_ and in _Synaptomys_. The baculum in these two genera in comparison to that in _Myopus_ (as figured by Ognev, 1948:512) and _Lemmus_ has a slenderer stalk and smaller digital ossifications or none at all. The baculum in the genera of lemmings increases in robustness and the development of processes from _Dicrostonyx_, to _Synaptomys_, to _Myopus_, to _Lemmus_--the same order outlined above for total of specialization. The two extremes in this series are near the extremes of variation in bacula to be found in all microtines. The baculum in lemmings as a group cannot then be considered more primitive than in voles as a group, although the voles are usually considered to be more advanced. The situation in the voles, as we shall see, casts a different light on the matter.

The voles, Tribe Microti, were considered by Hinton (1926:40) to be more advanced than the lemmings because the incisors of the voles are longer and the root of their last lower molar is lingual to the root of the incisor. Hinton thought also that the murine ancestors of microtines had shorter incisors and that the backward extension of the incisors in the voles is a more ancient feature than the hypsodonty of the molars. A trend in the molar teeth has been toward greater hypsodonty. The voles in which the molars are least hypsodont are thus considered primitive. These include the living genera _Clethrionomys_, _Phenacomys_, _Ondatra_, _Dolomys_, _Ellobius_, and _Prometheomys_. Therefore, the baculum, in these assumedly primitive genera, would be expected to resemble the baculum in the lemmings or at least the most primitive lemmings. This is not the case.

The bacula that I have examined of _Clethrionomys_ and _Phenacomys_ have well-developed digital ossifications. In this they resemble the baculum of the genus _Lemmus_, the most advanced genus of lemmings according to Hinton. The baculum of _Dolomys_ has not been studied. The baculum in _Ondatra_, and in _Prometheomys_ as illustrated by Ognev (1948:552), also possesses well-developed processes. The baculum of _Ellobius_ is small and lacks processes (as figured by Ognev, 1950:662). No ossification was found in a single specimen of _Ellobius_ examined by me although the entire glans penis was removed and cleared without dissection. So far as known then, with the exception of _Ellobius_ and _Phenacomys longicaudus_ (Dearden, 1958:547), the primitive microtines having rooted molars possess bacula having three well-developed ossified processes.

Voles of the genus _Microtus_ vary in the structure of the baculum almost as much as do the lemmings. Within the single subgenus _Microtus_ some individuals of _Microtus mexicanus_, for example, have minute ossified lateral processes and other individuals lack these processes; _Microtus pennsylvanicus_ and some other species have proportionately large lateral ossifications. If the well-developed condition of the baculum in the microtines having rooted molars is primitive, then within the genus _Microtus_ those species having well-developed bacula may be considered primitive.

The genera _Lagurus_ and _Neofiber_ have moderately developed or well-developed lateral processes. _Neofiber_ exhibits a tendency, not prominent elsewhere, to have a proportionately smaller median process rather than reduced lateral processes.

American species of _Microtus_ (genus and subgenus) that have moderately- to well-developed ossified lateral processes are _M. townsendii_, _M. oeconomus_, _M. pennsylvanicus_, _M. montanus_, and _M. chrotorrhinus_. _Microtus_ of other subgenera having this type of baculum include _M. (Herpetomys) guatemalensis_, _M. (Chilotus) oregoni_, and _M. (Chionomys) longicaudus_.

American species of _Microtus_ (genus and subgenus) in which the lateral ossifications are weakly developed or absent (although cartilaginous lateral processes are present) include _M. mexicanus_ and _M. californicus_. In other subgenera, species of _Microtus_ having reduced lateral ossifications are _M. (Pedomys) ochrogaster_, _M. (Pitymys) pinetorum_, _M. (Pitymys) parvulus_, _M. (Pitymys) quasiater_, _M. (Arvicola) richardsoni_, and _M. (Stenocranius) miurus_.

The microtines are essentially holarctic in distribution. Both of the tribes, the lemmings and the voles, as well as primitive representatives of each tribe (not considering _Ellobius_) occur in both the Old World and New World. It is not certain on which continent (or continents) the Microtinae first differentiated. It is certain, however, that at various times, both early and late in the evolution of the subfamily, representatives have crossed from Eurasia to North America or _vice versa_. Each of 10 or more microtines in the New World is more closely related to some microtine in the Old World than to any other microtine in the New World.

The similarities or differences in the baculum in Old World and New World representatives placed in the same genus or subgenus, or thought to be "companion species" have been commented upon in accounts of _Lemmus_, _Dicrostonyx_, _Clethrionomys_, _Lagurus_, _Arvicola_, _Stenocranius_, _Chilotus_, _Chionomys_, _Pitymys_, and in accounts of _Microtus agrestis_ as compared with _M. pennsylvanicus_, and _Microtus oeconomus_ (both Old World and New World).

The baculum in the Microtinae more closely resembles the baculum in the Cricetinae of the Old World than in the Murinae, or than in any other rodents known to me. This resemblance suggests relationship between Microtinae and Cricetinae.

LITERATURE CITED

ARGYROPULO, A. I.

1933a. Die Gattungen und Arten der Hamster (_Cricetinae_ Murray, 1866)
der Palaearktik. Zeitschr. f. Saeugetierkunde, 8:129-149, 27 figs. in
text.

1933b. Ueber zwei neue palaearktische Wuehlmaeuse. Zeitschr. f.
Saeugetierkunde, 8:180-183, 3 figs. in text.

CALLERY, R.

1951. Development of the os genitale in the golden hamster,
_Mesocricetus (Cricetus) auratus_. Jour. Mamm., 32:204-207, 1 fig. in
text.

CHAMBERLAIN, J. L.

1954. The Block Island meadow mouse, _Microtus provectus_. Jour. Mamm.,
35:587-589, 2 tables in text.

DEARDEN, L. C.

1958. The baculum in _Lagurus_ and related microtines. Jour. Mamm.,
39:541-553, 1 fig. in text.

DIDIER, R.

1943. L'os penien des Campagnols de France du Genre _Arvicola_.
Mammalia, 7:74-79, 10 figs. in text.

1954. Etude systematique de l'os penien des Mammiferes (suite),
Rongeurs: Murides. Mammalia, 18:237-256, 14 figs. in text.

ELLERMAN, J. R.

1941. The families and genera of living rodents. Vol. II. Family
Muridae. The British Museum (Natural History), London, pp. xii + 690,
50 figs.

FRILEY, CHARLES E.

1947. Preparation and preservation of the baculum of mammals. Jour.
Mamm., 28:395-397, 1 fig. in text.

HALL, E. R., and E. L. COCKRUM.

1953. A synopsis of the North American microtine rodents. Univ. Kansas
Publ., Mus. Nat. Hist., 5:373-498, 149 figs. in text.

HAMILTON, W. J., JR.

1946. A study of the baculum in some North American Microtinae. Jour.
Mamm., 27:378-387, 3 figs. in text.

HIBBARD, C. W., and G. C. RINKER.

1942. A new bog-lemming (Synaptomys) from Meade County, Kansas. Univ.
Kansas Sci. Bull., 28:25-35, 3 figs. in text.

1943. A new meadow mouse (_Microtus ochrogaster taylori_) from Meade
County, Kansas. Univ. Kansas Sci. Bull., 29:255-268, 5 figs. in text.

HINTON, M. A. C.

1926. Monograph of the voles and lemmings (Microtinae), living and
extinct, Vol. I. British Museum (Natural History), London, pp. xvi +
488, plus 15 plates, 110 figs. in text.

MATTHEY, R.

1953. Les Chromosomes des Muridae. Revue Suisse de Zoologie,
60:225-283, avec les planches 1 a 4 groupant 84 photomicrographies, 98
figures et 5 schemas dans le texte.

1955. Nouveaux documents sur les chromosomes des Muridae. Problemes de
cytologie comparee et de taxonomie chez les Microtinae. Revue Suisse de
Zoologie, 62:163-206, avec 114 figures.

MILLER, G. S.

1896. Genera and subgenera of voles and lemmings. North American Fauna
No. 12, pp. 1-85, 40 figs. and 3 plates in text.

OGNEV, S. I.

1948. The mammals of Russia (USSR) and adjacent countries (The mammals
of Eastern Europe and Northern Asia), Vol. 6. Publ. Acad. Sci. USSR,
pp. 1-587, 260 figs., 12 maps, and 11 color plates in text (in
Russian).

1950. The mammals of Russia (USSR) and adjacent countries (The mammals
of Eastern Europe and Northern Asia), Vol. 7. Publ. Acad. Sci. USSR,
pp. 1-736, 347 figs., 15 maps, and 10 color plates in text (in
Russian).

RUTH, E. B.

1934. The os priapi: A study in bone development. Anat. Rec.,
60:231-249, 16 figs. in 3 plates.

SMITH, D. A., and J. B. FOSTER.

1957. Notes on the small mammals of Churchill, Manitoba. Jour. Mamm.,
38:98-115, 3 figs. and 3 tables in text.

WHEELER, B.

1956. Comparison of the Block Island "species" of _Microtus_ with _M.
pennsylvanicus_. Evolution, 10:176-186, 4 figs. and 2 tables in text.

WHITE, J. A.

1951. A practical method for mounting the bacula of small mammals.
Jour. Mamm., 32:125.

ZIMMERMAN, K.

1955. Die Gattung _Arvicola_ Lac. im System der Microtinae.
Saeugetierkundliche Mitteilungen, 3:110-112, 2 figs. in text.

_Transmitted August 14, 1959._

28-774

UNIVERSITY OF KANSAS PUBLICATIONS
MUSEUM OF NATURAL HISTORY

Institutional libraries interested in publications exchange may obtain this series by addressing the Exchange Librarian, University of Kansas Library, Lawrence, Kansas. Copies for individuals, persons working in a particular field of study, may be obtained by addressing instead the Museum of Natural History, University of Kansas, Lawrence, Kansas. There is no provision for sale of this series by the University Library which meets institutional requests, or by the Museum of Natural History which meets the requests of individuals. However, when individuals request copies from the Museum, 25 cents should be included, for each separate number that is 100 pages or more in length, for the purpose of defraying the costs of wrapping and mailing.

* An asterisk designates those numbers of which the Museum's supply (not the Library's supply) is exhausted. Numbers published to date, in this series, are as follows:

Vol. 1. Nos. 1-26 and index. Pp. 1-638, 1946-1950.

*Vol. 2. (Complete) Mammals of Washington. By Walter W. Dalquest. Pp.
1-444, 140 figures in text. April 9, 1948.

Vol. 3. *1. The avifauna of Micronesia, its origin, evolution, and
distribution. By Rollin H. Baker. Pp. 1-359, 16 figures in
text. June 12, 1951.

*2. A quantitative study of the nocturnal migration of birds.
By George H. Lowery, Jr. Pp. 361-472, 47 figures in text. June
29, 1951.

3. Phylogeny of the waxwings and allied birds. By M. Dale
Arvey. Pp. 473-530, 49 figures in text, 13 tables. October 10,
1951.

4. Birds from the state of Veracruz, Mexico. By George H.
Lowery, Jr., and Walter W. Dalquest. Pp. 531-649, 7 figures in
text, 2 tables. October 10, 1951.

Index. Pp. 651-681.

*Vol. 4. (Complete) American weasels. By E. Raymond Hall. Pp. 1-466, 41
plates, 31 figures in text. December 27, 1951.

Vol. 5. Nos. 1-37 and index. Pp. 1-676, 1951-1953.

*Vol. 6. (Complete) Mammals of Utah, _taxonomy_ and _distribution_. By
Stephen D. Durrant. Pp. 1-549, 91 figures in text, 30 tables.
August 10, 1952.

Vol. 7. *1. Mammals of Kansas. By E. Lendell Cockrum. Pp. 1-303, 73
figures in text, 37 tables. August 25, 1952.

2. Ecology of the opossum on a natural area in northeastern
Kansas. By Henry S. Fitch and Lewis L. Sandidge. Pp. 305-338,
5 figures in text. August 24, 1953.

3. The silky pocket mice (Perognathus flavus) of Mexico. By
Rollin H. Baker. Pp. 339-347, 1 figure in text. February 15,
1954.

4. North American jumping mice (Genus Zapus). By Phillip H.
Krutzsch. Pp. 349-472, 47 figures in text, 4 tables. April 21,
1954.

5. Mammals from Southeastern Alaska. By Rollin H. Baker and
James S. Findley. Pp. 473-477. April 21, 1954.

6. Distribution of Some Nebraskan Mammals. By J. Knox Jones,
Jr. Pp. 479-487. April 21, 1954.

7. Subspeciation in the montane meadow mouse, Microtus
montanus, in Wyoming and Colorado. By Sydney Anderson. Pp.
489-506, 2 figures in text. July 23, 1954.

8. A new subspecies of bat (Myotis velifer) from southeastern
California and Arizona. By Terry A. Vaughan. Pp. 507-512. July
23, 1954.

9. Mammals of the San Gabriel mountains of California. By
Terry A. Vaughan. Pp. 513-582, 1 figure in text, 12 tables.
November 15, 1954.

10. A new bat (Genus Pipistrellus) from northeastern Mexico.
By Rollin H. Baker. Pp. 583-586. November 15, 1954.

11. A new subspecies of pocket mouse from Kansas. By E.
Raymond Hall. Pp. 587-590. November 15, 1954.

12. Geographic variation in the pocket gopher, Cratogeomys
castanops, in Coahuila, Mexico. By Robert J. Russell and
Rollin H. Baker. Pp. 591-608. March 15, 1955.

13. A new cottontail (Sylvilagus floridanus) from
northeastern Mexico. By Rollin H. Baker. Pp. 609-612. April 8,
1955.

14. Taxonomy and distribution of some American shrews. By
James S. Findley. Pp. 613-618. June 10, 1955.

15. The pigmy woodrat, Neotoma goldmani, its distribution and
systematic position. By Dennis G. Rainey and Rollin H. Baker.
Pp. 619-624, 2 figures in text. June 10, 1955.

Index. Pp. 625-651.

Vol. 8. 1. Life history and ecology of the five-lined skink, Eumeces
fasciatus. By Henry S. Fitch. Pp. 1-156, 26 figures in text.
September 1, 1954.

2. Myology and serology of the Avian Family Fringillidae, a
taxonomic study. By William B. Stallcup. Pp. 157-211, 23
figures in text, 4 tables. November 15, 1954.

3. An ecological study of the collared lizard (Crotaphytus
collaris). By Henry S. Fitch. Pp. 213-274, 10 figures in text.
February 10, 1956.

4. A field study of the Kansas ant-eating frog, Gastrophryne
olivacea. By Henry S. Fitch. Pp. 275-306, 9 figures in text.
February 10, 1956.

5. Check-list of the birds of Kansas. By Harrison B. Tordoff.
Pp. 307-359, 1 figure in text. March 10, 1956.

6. A population study of the prairie vole (Microtus
ochrogaster) in northeastern Kansas. By Edwin P. Martin. Pp.
361-416, 19 figures in text. April 2, 1956.

7. Temperature responses in free-living amphibians and
reptiles of northeastern Kansas. By Henry S. Fitch. Pp.
417-476, 10 figures in text, 6 tables. June 1, 1956.

8. Food of the crow, Corvus brachyrhynchos Brehm, in
south-central Kansas. By Dwight Platt. Pp. 477-498, 4 tables.
June 8, 1956.

9. Ecological observations on the woodrat Neotoma floridana.
By Henry S. Fitch and Dennis G. Rainey. Pp. 499-533, 3 figures
in text. June 12, 1956.

10. Eastern woodrat, Neotoma floridana; Life history and
ecology. By Dennis G. Rainey. Pp. 535-646, 12 plates, 13
figures in text. August 15, 1956.

Index. Pp. 647-675.

Vol. 9. 1. Speciation of the wandering shrew. By James S. Findley. Pp.
1-68, 18 figures in text. December 10, 1955.

2. Additional records and extension of ranges of mammals from
Utah. By Stephen D. Durrant, M. Raymond Lee, and Richard M.
Hansen. Pp. 69-80. December 10, 1955.

3. A new long-eared myotis (Myotis evotis) from northeastern
Mexico. By Rollin H. Baker and Howard J. Stains. Pp. 81-84.
December 10, 1955.

4. Subspeciation in the meadow mouse, Microtus
pennsylvanicus, in Wyoming. By Sydney Anderson. Pp. 85-104, 2
figures in text. May 10, 1956.

5. The condylarth genus Ellipsodon. By Robert W. Wilson. Pp.
105-116, 6 figures in text. May 19, 1956.

6. Additional remains of the multituberculate genus
Eucosmodon. By Robert W. Wilson. Pp. 117-123, 10 figures in
text. May 19, 1956.

7. Mammals of Coahuila, Mexico. By Rollin H. Baker. Pp.
125-335, 75 figures in text. June 15, 1956.

8. Comments on the taxonomic status of Apodemus peninsulae,
with description of a new subspecies from North China. By J.
Knox Jones, Jr. Pp. 337-346, 1 figure in text, 1 table. August
15, 1956.

9. Extensions of known ranges of Mexican bats. By Sydney
Anderson. Pp. 347-351. August 15, 1956.

10. A new bat (Genus Leptonycteris) from Coahuila. By Howard
J. Stains. Pp. 353-356. January 21, 1957.

11. A new species of pocket gopher (Genus Pappogeomys) from
Jalisco, Mexico. By Robert J. Russell. Pp. 357-361. January
21, 1957.

12. Geographic variation in the pocket gopher, Thomomys
bottae, in Colorado. By Phillip M. Youngman. Pp. 363-387, 7
figures in text. February 21, 1958.

13. New bog lemming (genus Synaptomys) from Nebraska. By J.
Knox Jones, Jr. Pp. 385-388. May 12, 1958.

14. Pleistocene bats from San Josecito Cave, Nuevo Leon,
Mexico. By J. Knox Jones, Jr. Pp. 389-396. December 19, 1958.

15. New subspecies of the rodent Baiomys from Central
America. By Robert L. Packard. Pp. 397-404. December 19, 1958.

16. Mammals of the Grand Mesa, Colorado. By Sydney Anderson.
Pp. 405-414, 1 figure in text, May 20, 1959.

17. Distribution, variation, and relationships of the montane
vole, Microtus montanus. By Sydney Anderson. Pp. 415-511, 12
figures in text, 2 tables. August 1, 1959.

18. Conspecificity of two pocket mice, Perognathus goldmani
and P. artus. By E. Raymond Hall and Marilyn Bailey Ogilvie.
Pp. 513-518, 1 map in text. January 14, 1960.

19. Records of harvest mice, Reithrodontomys, from Central
America, with description of a new subspecies from Nicaragua.
By Sydney Anderson and J. Knox Jones, Jr. Pp. 519-529. January
14, 1960.

20. Small carnivores from San Josecito Cave (Pleistocene),
Nuevo Leon, Mexico. By E. Raymond Hall. Pp. 531-538, 1 figure
in text. January 14, 1960.

21. Pleistocene pocket gophers from San Josecito Cave, Nuevo
Leon, Mexico. By Robert J. Russell. Pp. 539-548, 1 figure in
text, January 14, 1960. More numbers will appear in volume 9.

Vol. 10. 1. Studies of birds killed in nocturnal migration. By Harrison
B. Tordoff and Robert M. Mengel. Pp. 1-44, 6 figures in text,
2 tables. September 12, 1956.

2. Comparative breeding behavior of Ammospiza caudacuta and
A. maritima. By Glen E. Woolfenden. Pp. 45-75, 6 plates, 1
figure. December 20, 1956.

3. The forest habitat of the University of Kansas Natural
History Reservation. By Henry S. Fitch and Ronald R. McGregor.
Pp. 77-127, 2 plates, 7 figures in text, 4 tables. December
31, 1956.

4. Aspects of reproduction and development in the prairie
vole (Microtus ochrogaster). By Henry S. Fitch. Pp. 129-161, 8
figures in text, 4 tables. December 19, 1957.

5. Birds found on the Arctic slope of northern Alaska. By
James W. Bee. Pp. 163-211, plates 9-10, 1 figure in text.
March 12, 1958.

6. The wood rats of Colorado: distribution and ecology. By
Robert B. Finley, Jr. Pp. 213-552, 34 plates, 8 figures in
text, 35 tables. November 7, 1958.

7. Home ranges and movements of the eastern cottontail in
Kansas. By Donald W. Janes. Pp. 553-572, 4 plates, 3 figures
in text. May 4, 1959.

8. Natural history of the salamander Aneides hardyi. By
Richard F. Johnston and Gerhard A. Schad. Pp. 573-585. October
8, 1959.

More numbers will appear in volume 10.

Vol. 11. 1. The systematic status of the colubrid snake, Leptodeira
discolor Guenther. By William E. Duellman. Pp. 1-9, 4 figures.
July 14, 1958.

2. Natural history of the six-lined racerunner, Cnemidophorus
sexlineatus. By Henry S. Fitch. Pp. 11-62, 9 figures, 9
tables. September 19, 1958.

3. Home ranges, territories, and seasonal movements of
vertebrates of the Natural History Reservation. By Henry S.
Fitch. Pp. 63-326, 6 plates, 24 figures in text, 3 tables.
December 12, 1958.

4. A new snake of the genus Geophis from Chihuahua, Mexico.
By John M. Legler. Pp. 327-334, 2 figures in text. January 28,
1959.

5. A new tortoise, genus Gopherus, from north-central Mexico.
By John M. Legler. Pp. 335-343. April 24, 1959.

6. Fishes of Chautauqua, Cowley and Elk counties, Kansas. By
Artie L. Metcalf. Pp. 345-400, 2 plates, 2 figures in text, 10
tables. May 6, 1959.

7. Fishes of the Big Blue River Basin, Kansas. By W. L.
Minckley. Pp. 401-442, 2 plates, 4 figures in text, 5 tables.
May 8, 1959.

8. Birds from Coahuila, Mexico. By Emil K. Urban. Pp.
443-516. August 1, 1959.

9. Description of a new softshell turtle from the
southeastern United States. By Robert G. Webb. Pp. 517-525, 2
plates, 1 figure in text. August 14, 1959.

Another number will appear in volume 11.

Vol. 12. 1. Functional morphology of three bats: Eumops, Myotis,
Macrotus. By Terry A. Vaughan. Pp. 1-153, 4 plates, 24 figures
in text. July 8, 1959.

2. The ancestry of modern Amphibia: a review of the evidence.
By Theodore H. Eaton, Jr. Pp. 155-180, 10 figures in text.
July 10, 1959.

3. The baculum in microtine rodents. By Sydney Anderson. Pp.
181-216, 49 figures in text. February 19, 1960.

More numbers will appear in volume 12.