Baculum: Stalk elongate, greatest length (2.8 mm.) 2-1/2 times greatest breadth, 6 times greatest depth; three well-developed ossified processes; median process larger than lateral processes, 1/2 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 1/2 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. Clethrionomys glareolus Schreber Fig. 13 Baculum: Stalk elongate, greatest length (2.9 mm.) twice the greatest breadth in the specimen examined, flattened proximally, greatest length almost 6 times greatest depth of base; three well-developed ossified processes; median process arched in a dorsoventral plane, with basal notch and lateral lobes; lateral processes as long as median process, bowed in dorsal view, flattened distally, with ventromedial vane; basal tuberosities of stalk weakly developed, medially confluent; posterior profile in dorsal view evenly rounded; in end-view dorsal concavity shallow in comparison to most species but deeper than ventral concavity, constriction 3/4 greatest depth; shaft straight, at mid-point slightly wider than high, elongate, widest point of stalk less than 1/4 of total length from proximal end, slight lateral inflation at tip; lateral profile in dorsal view sloping at first abruptly and then gradually from widest point of stalk anteriorly onto shaft.