Microtus (Stenocranius) miurus Osgood Figs. 32 and 33 Baculum: Length of stalk (2.8 mm.) 1-1/2 times greatest breadth, 3-1/2 times greatest depth; median process ossified, 2/5 to 3/5 length of stalk, laterally compressed, sometimes arched in dorsoventral plane; lateral processes cartilaginous, slender; basal tuberosities well developed, averaging less enlarged than shown in Figure 32, but more angular in lateral outline than shown in Figure 33; tuberosities confluent posteriorly; posterior profile smoothly rounded to trilobate, curvature at point of greatest breadth usually acute; in proximal end-view base wider dorsally, deep dorsal concavity, shallow ventral concavity, medial constriction 3/5 of greatest depth; shaft slender anteriorly, at mid-point of stalk twice as wide as high, at tip higher than wide, laterally inflated; lateral profile in most specimens abruptly curved anterior to point of greatest breadth. The single specimen of the Old World _M. (Stenocranius) gregalis_ examined resembles the New World _M. (Stenocranius) miurus_ in the angular lateral profile at the point of greatest breadth of the stalk, slender shaft in comparison to broad base of stalk, and presence of a single well-developed laterally compressed median process. The base of the stalk in the baculum of _M. gregalis_ is less well developed and smaller than in the baculum of _M. miurus_. _Specimens examined_: Nine, all of the subspecies _Microtus miurus muriei_, from the Brooks Range, Alaska; 51077 (Lake Schrader, 145°09'50", 69°24'28", 2900 ft., Romanzof Mts.); 51151, 51152, 51154, 51164, 51166, 51169 (last 6 from Wahoo Lake, 69°08', 146°58', 2350 ft.); 51210, 51213 (last 2 from Porcupine Lake, 68°51'57", 146°29'50", 3140 ft.). Microtus (Chionomys) nivalis Martins Fig. 47 Baculum: Greatest length of stalk (2.7 mm.) 2-1/4 times greatest breadth, 4-1/2 times greatest depth; three digitate processes, lateral processes mostly cartilaginous in single adult examined; median process well ossified, approximately 1/3 length of stalk, basally notched, not arched, laterally compressed distally; base of stalk broad and flat, basal tuberosities well developed, separate; posterior profile in dorsal view rounded, convex except for medial notch separating tuberosities; dorsal and ventral concavities deep, broad, equal; medial constriction less than 1/2 greatest depth; in dorsal view shaft tapering gradually from widest point, terminally rounded; at mid-point of stalk almost twice as wide as high. In the elongate, largely cartilaginous lateral processes of the baculum, the specimen described above resembles _M. longicaudus_. The size of the median process in comparison to the size of the stalk is also the same. The lateral processes have larger ossifications and the base of the stalk is more robust in _M. longicaudus_ than in _M. nivalis_.