_Color._--Winter pelage unknown. Summer pelage with upper parts near (14 n) Brussels Brown or tone 2 of Raw Umber of Oberthür and Dauthenay, Pl. 301, darker on top of head from nose to line connecting posterior margins of ears. Tip of tail always black. Chin and upper lips white. Remainder of underparts Buff Yellow to Straw Yellow and rarely Ochraceous Buff. Color of underparts extends distally on posterior sides of forelegs over toes onto antipalmar faces of feet and wrists, on medial sides of hind legs to ankles and over antiplantar faces of toes, medial third of tarsus, and over proximal fifth to fourth of ventral side of tail. Least width of color of underparts averaging, in 8 specimens, 44 (29-54) per cent of greatest width of color of upper parts. Black tip of tail, in four females averaging 35 (33-38) mm. long. Thus, averaging shorter than hind foot and 32 per cent of length of tail-vertebrae. Three of the eight specimens before me (no. 242671 from 25 mi. SE Flagstaff, not available at time of this accounting) have the dark spot near the angle of the mouth faintly indicated, whereas the other five lack the spots. The color is as in _M. f. nevadensis_. _Skull and teeth._--Male (based on 55211, 65231, and 248993; see p. 422): See measurements and plates 19-21; weight 2.7 and 3.1 grams; basilar length, 40.4; zygomatic breadth more than distance between condylar foramen and Ml or than between anterior palatine foramen and anterior margin of tympanic bulla; mastoid breadth more than postpalatal length; postorbital breadth less than length of upper premolars and more than width of basioccipital measured from medial margin of one foramen lacerum posterior to its opposite; interorbital breadth more or less than distance between foramen opticum and anterior margin of tympanic bulla; breadth of rostrum less than length of tympanic bulla; least width of palate more or less than medial length of P4; anterior margin of tympanic bulla as far posterior to foramen ovale as width of 3-1/2 (including I3) upper incisors; height of tympanic bulla more than distance from its anterior margin to foramen ovale; length of tympanic bulla more than length of lower molar-premolar tooth-row and longer or shorter than rostrum; anterior margin of masseteric fossa below talonid of m1.