22 University of California PuMications in Zoology [Vol. 21 



42; Kearsarge Pass (Grays), 15; Independence, 30; Laws, 5; Silver 

 Canon (3 miles E Laws), 3. Mono County: Benton, 1. 



Diagnosis. — Size large (hind foot, 21 to 25 mm., eondylobasal 

 length of skull in largest individuals, 31.6 mm.) ; second upper molar 

 with open posterior internal lobe or loop ; skull long, but narrower 

 and not as strongly ridged as in aestuarinus (ratio of zygomatic 

 breadth to eondylobasal length about 57%) ; interorbital region with 

 poorly developed ridges. Colors dark. 



Color. — Mass effect of dorsal area dull sepia, peppered with black, 

 or darkened by an admixture of long overhairs, most pronounced mid- 

 dorsally. In fresh pelage: Hairs of upperparts blackish plumbeous 

 basally, with light tippings varying from pinkish buff to light buff; 

 long overhairs ranging from light seal brown to dark aniline black. 

 The light tips of the hairs on the sides become lighter and more buffy, 

 passing abruptly into color of underparts. Rump may show a stronger 

 infusion of light tipped hairs than rest of upperparts. Underparts 

 pallid neutral gray, occasionally with a slight wash of buffy, the 

 plumbeous of hair bases everywhere showing through at surface. 

 Anal area whitish. Terminal portions of whiskers whitish, with bases 

 darker. Nose usually darker than area in front of eyes. Ears rather 

 large, not concealed by fur, with anterior border darkened by the 

 plumbeous hair bases. Tail distinctly bicolor, dark aniline black above 

 and pallid mouse gray below. Hands and feet covered with pallid 

 mouse gray hairs. In worn pelage : Mass effect dull buffy or grayish 

 (moldy appearance), with little infusion of long dark overhairs. The 

 slate gray hair bases show through and take part in the general 

 coloration. Tail distinctly bicolor. 



Skull. — Essentially the same length as in aestuarinus, but narrower 

 and less robust ; larger and less angular in old age than in calif ornicus. 

 Dorsal profile with a more uniform convexity than shown by other 

 members of this group. Occiput more abruptly truncate, concealing 

 the condyles for the most part from above. Ventral profile similar 

 to that in calif ornicus. 



From a dorsal aspect the brain-case is distinctly rounded at sides, 

 and truncated anteriorly by strongly developed postorbital tuberosi- 

 ties, which project winglike over orbital fossae. In old adults there 

 are well developed longitudinal ridges near edges of parietals. The 

 interorbital region is rather broad, with a distinct median sulcus, but 

 with interorbital ridges well defined. Lambdoidal ridge similar to 

 that of aestuarinus. Interparietal subrectangular, its posterior border 

 variable, but usually somewhat convex, its lateral extremities rather 

 abruptly truncate. Anteroposterior diameter of interparietal, exclu- 

 sive of median projection, less than one-half of greatest transverse 

 diameter. Frontals occasionally convex posteriorly, but usually 

 truncate or even emarginate. 



Width of rostrum at narrowest region slightly greater than breadth 

 of interorbital constriction. Least depth behind incisors usually 

 greater than, but sometimes equal to, width in same region. Nasals 

 broad at anterior ends, narrowing uniformly toward posterior ends, 

 but with their terminations emarginate in some individuals while in 

 others rounded and notched. In all skulls examined the nasals were 

 slightly exceeded by ascending branches of premaxillae. Opening 



