_Color._--Upper parts, in summer, Brussels Brown to near (14 _n_) Brussels Brown, or tones 2 to 4 of Raw Umber of Oberthür and Dauthenay, pl. 301. Chin and rarely upper lips white. Remainder of underparts Picric Yellow to Primuline Yellow. In winter, color essentially the same except for smoke-gray effect in upper parts and more whitish in underparts. Tip of tail at all times black. Upper parts of uniform color except for occasional darkening of nose and mid-dorsal region. Color of underparts extends distally on posterior sides of forelegs onto antipalmar faces of toes, on medial sides of hind legs only to a point between knee and ankle. Least width of color of underparts averaging, in a series of 21 males from Lawrence, Kansas, 23 (9-35) per cent of greatest width of color of upper parts. Black tip of tail in same series, most of which are in full winter pelage, 52 (40-70) mm. long; thus longer than hind foot and averaging 39 per cent of length of tail-vertebrae. _Skull and teeth._--Male (based on ten adults from Douglas County, Kansas): See measurements and plates 16-18; weight, 3.7 (3.3-4.2) grams; basilar length, 44.8 (43.8-46.0); zygomatic breadth more or less (less in 80 per cent) than distance between condylar foramen and M1 or than between anterior palatine foramen and anterior end of tympanic bulla (less in 70 per cent); mastoid breadth more or less (less in 80 per cent) than postpalatal length; postorbital breadth less than length of upper premolars and, except in one specimen, more than width of basioccipital measured from medial margin of one foramen lacerum posterior to its opposite; interorbital breadth more or less (less in 70 per cent) than distance between foramen opticum and anterior margin of tympanic bulla; breadth of rostrum less than length of tympanic bulla; least width of palate less than outside length of P4 (except in one specimen); anterior margin of tympanic bulla as far posterior to foramen ovale as width of 2-1/2 to 5 upper incisors; height of tympanic bulla more (except in one specimen) than distance from its anterior margin to foramen ovale; length of tympanic bulla more than length of lower molar and premolar tooth-row and longer (except in one specimen) than rostrum; anterior margin of masseteric fossa behind or just below posterior eighth of m1.