Baculum: Stalk elongate, greatest length (2.7 to 2.8 mm.) 2-1/3 to 2-1/2 times greatest breadth, 4 to 5 times greatest depth; three processes ossified or lateral processes unossified, ossifications relatively small (in 78380, median ossification less than 1/4 as large as lateral ossifications although median cartilaginous process is larger), length of median process 1/5 to 1/6 of length of stalk, cartilaginous part of median process larger; posterior profile in dorsal view convex throughout or bilobate; tuberosities moderately developed, deflected dorsal to axis of shaft; in end-view medial construction 3/5 greatest depth of tuberosities; shaft tapered from point of greatest width, slightly inflated terminally. The specimen (KU 13716) figured by Hibbard and Rinker (1942:29) has been restudied. It was first cleared and stained to soften the dry cartilage binding the digital processes together and to differentiate bone and cartilage. The lateral processes are small and cartilaginous (Fig. 6) and seem intact. The differences between this specimen and others examined by Hamilton (1946:381), Dearden (1958:542), and myself, namely the relatively larger median ossification, the absence of ossification in lateral processes, and the distinctly bilobate base and larger size, may represent geographic differences, or individual variation. The proportions of length, width, and depth of the stalk, and the appearance in lateral view do not differ greatly from others examined by Hamilton, by Dearden (1958:546), and by me. _Specimens examined_: Five, representing four subspecies; _S. cooperi gossii_, 6 mi. N Midway, Holt Co., Nebraska 78379, 78380; _S. cooperi relictus_, 5 mi. N, 2 mi. W Parks, Dundy Co., Nebraska, 72601 (immature); _S. cooperi saturatus_, 3 mi. S Demotte, Jasper Co., Indiana, 3-C-454, collection of W. B. Quay; _S. cooperi paludis_, Meade County State Park, Kansas, 13716. Clethrionomys rutilus Pallas Fig. 11 Baculum: Stalk elongate, and proximally enlarged, greatest length (2.7 mm.) 2 times greatest breadth; less than 4 times greatest depth; three well-developed ossified processes; length of stalk 2-1/3 times length of median process; median process with basal (and ventral) protuberence and lateral lobes, arched in dorsoventral plane; lateral processes as large as median process, flattened distally, having ventromedial vane on distal half; basal tuberosities of stalk well developed, medially confluent; posterior profile in dorsal view trilobate or convex throughout with rounded posterior apex; dorsal concavity well developed, ventral surface but slightly concave, medial constriction of base as little as 1/2 greatest depth; shaft straight, slender, at mid-point of stalk but slightly wider than high; basal tuberosities largely dorsal to axis of shaft in lateral view; lateral profile in dorsal view with an abrupt curvature separating the gently sloping sides of the shaft from the basal part at its greatest breadth.