10 University of California Puhlications in Zoology [Yoh. 21 



Diagnosis. — Size small (hind foot, 20 to 22 mm., condylobasal 

 length of skull in largest individuals, 28.1 mm. ) ; second upper molar 

 with or without posterior internal loop or lobe ; skull small, relatively- 

 narrow (ratio of zygomatic breadth to condylobasal length about 

 57%) ; intertemporal region developing a ridge with age; colors dull. 



Color. — General effect of dorsal area buckthorn brown, but duller 

 than in calif ornicus. Dorsal area often strongly mixed with dark over- 

 hairs, becoming somewhat buffy on sides, and everywhere rather con- 

 spicuously ' ' lined ' ' by the longer dark hairs. In fresh pelage : Hairs 

 of upperparts blackish plumbeous basally, with light tipped portions 

 grading from buckthorn brown to ochraceous-tawny ; the long over- 

 hairs grading from Mars brown to aniline black. Sides lighter than 

 upperparts, with light tipped portions of hairs approaching cinnamon 

 buff; rump much brighter than rest of upperparts. Underparts 

 washed with pallid neutral gray ; anal area -nearly pure white. Ter- 

 minal portions of whiskers largely whitish with darker bases. Upper 

 and sometimes lower lip whitish. Nose not conspicuously darker than 

 area in front of eyes. Ears moderate in size, not concealed by fur, 

 with anterior border furred with aniline black hairs or with hairs 

 tipped with buckthorn brown. Tail distinctly bicolor, usually light 

 mummy brown and pallid neutral gray beneath. Hands and feet 

 scantily covered with cinereous hairs, the dorsal surface of the foot 

 strongly contrasted with upper parts. In worn pelage : Duller, with 

 larger suffusion of dark tipped hairs. Tail almost concolor in some 

 specimens. 



Skull. — Except for its smaller size, the skull bears a general re- 

 semblance to that of calif ornicus. In size and certain peculiarities of 

 form it is more variable than other races of this group. Dorsal profile 

 about as in calif ornicus; occiput rounded, but concealing the occipital 

 condyles for the most part when skull is viewed from above ; ventral 

 profile sloping more obliquely than in californicus. 



Outline of brain-case viewed from above, subovate, wider ante- 

 riorly than posteriorly and large relatively to general size of skull. 

 Postorbital tuberosities usually small or inconspicuous, producing 

 no conspicuous break in contour of skull. In old adults longitudinal 

 ridges near outer edges of parietals are fairly well developed and unite 

 with interorbital ridges in frontal region. In appearance the inter- 

 orbital region is variable, but in most specimens of extreme old age 

 the interorbital ridges have not preserved their individuality, but have 

 coalesced, forming a single median ridge. Lambdoidal ridge similar 

 to that in eximius, but not as well developed. Interparietal variable 

 in appearance, in most cases strongly convex posteriorly and with 

 outer extremities rather obliquely truncate. Anteroposterior diam- 

 eter, exclusive of median projection, variable. Frontals convex or 

 truncate posteriorly, slightly elevated anteriorly. 



This form is best characterized by the short rostrum, somewhat 

 slender in immature individuals, but increasing in width with age 

 until in extreme old age width is almost equal to length. The least 

 depth behind incisors usually about equal to width in same region. 

 Nasals relatively long, slender, with anterior declivity decidedly 

 abrupt, widening slightly anterior to middle, strongly truncated at 

 posterior termination. Nasals sometimes notched posteriorly, falling 



