Part 4 (1/2)

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 Buchner

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 p.r.o.nounced (less than 1/2 greatest depth); lateral profile at widest point of stalk convex, becoming abruptly concave as the f.l.a.n.g.e 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 monta.n.u.s (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 monta.n.u.s amosus_, 1/2 mi. E Soldier Summit, Wasatch Co., Utah, 62241; _M. monta.n.u.s fusus_, La Manga Pa.s.s, 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 monta.n.u.s na.n.u.s_, 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., Was.h.i.+ngton, 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.