Microtus oeconomus (Pallas)
Fig. 44
Baculum: Stalk broad and flattened, greatest length (3.5 mm.) 12/3 to 2 times greatest width, 4 to 5½ 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.