The Baculum in Microtine Rodents

by Sydney Anderson

Clethrionomys occidentalis (Merriam)

Fig. 12

Baculum: Stalk elongate, greatest length (2.8 mm.) 2½ times greatest breadth, 6 times greatest depth; three well-developed ossified processes; median process larger than lateral processes, ½ 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 ½ 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.