_Characters for ready recognition._--Differs from _M. f. oregonensis_ in longer hind foot of males which is more than 50 mm., and in both sexes, larger, more prominently ridged skull (see measurements and plates); from _M. f. saturata_ by presence of nasofrontal white spot, larger and relatively shallower skull of males and larger skull of female; from _M. f. nevadensis_ by presence of well-developed, white, facial markings; absence of color of underparts on ventral face of proximal third of tail; and hind foot of males more than 50; from _M. f. xanthogenys_ by near (_l_) Sudan Brown to near (_l_) Antique Brown rather than Buckthorn Brown colors of upper parts and greater size, and in adult male basilar length more than 45 and hind foot more than 47; from _M. f. nigriauris_ by having inside of ears same color as back rather than much darker than back. _Description._--_Size._--Male: Three adults and two young from Point Arena and Gualala, Mendocino County, yield average and extreme measurements as follows: Total length, 447 (434-470); length of tail, 167 (150-185); length of hind foot, 53 (50-60). Corresponding measurements of three adults from 5 and 6 miles west of Inverness, Marin County, are: 430 (420-440), 154 (141-160), 48 (48-49). Corresponding measurements of four individuals (3 adults and 1 young of large size) from South Yolla Bolly Mountain, Trinity County, are: 383 (374-400), 134 (130-138); 44 (43-44). The tail averages 60 per cent as long as the head and body in the series from Point Arena, 56 per cent in the series from Point Reyes, and 53 per cent in the series from South Yolla Bolly Mountain. In every specimen except two, length of hind foot less than basal length. The two exceptions are no. 19720, M.V.Z., male adult from Point Arena in which the hind foot is recorded as 60 (probably an error in measurement), and no. 19721, M.V.Z., from the same place, in which the skull has not yet attained its full growth. Female: One adult from Point Arena measures as follows: Total length, 383; length of tail, 134; length of hind foot, 43. Corresponding measurements of an adult from seven miles north of Laytonville, Mendocino County, are: 336, 121, 33 (= 36 on dried skin). Corresponding measurements of an adult from South Yolla Bolly Mountain, Trinity County, are, 326, 113, 37. In these three specimens, the tail is, in the order given, 54, 56, and 53 per cent as long as the head and body. Length of hind foot more than basal length. Differences in external measurements of the two sexes as indicated by the five males and one female from Point Arena, are: Total length, 64; length of tail, 33; length of hind foot, 10. Weights of 2 adult males are 265 and 221 grams and of one adult female 155 grams.