Microtus arvalis (Pallas)
Fig. 22
Baculum: In the single specimen examined, stalk small, greatest length (2.3 mm.) 21/3 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.