1922] Kellogg: Calif or nian Forms of Microtus Montanus 269 



Color. — Mass effect of dorsal area ranging from sayal brown to 

 light natal brown, with varying admixture of long, blackish overhairs. 

 In fresh pelage : hairs of upperparts blackish plumbeous basalh', with 

 light tipped portion grading from clay color to snuff brown. Sides 

 much lighter than middorsum, with larger proportion of buffy or 

 clay color tipped hairs. Rump usually the same color, seldom brighter 

 than rest of upperparts. Underparts pallid neutral gray, usually with 

 faint suffusion of buify, dulled by irregular appearance of basal under- 

 fur. Whiskers either white or light aniline black. Nose slightly darker 

 than area between the eyes. Ears relativel.y smaller, not concealed by 

 fur, and with anterior border less heavily- furred than in yosemite. 

 Tail distinctly bicolor, aniline black above and varying from pale 

 olive buff to mouse gray below. Hands and feet covered with hairs 

 ranging in color in different individuals from light drab to light 

 mouse gray. In worn pelage : upperparts usually duller, lighter, and 

 with an apparent diminution of the number of long, dark overhairs 

 present. 



SJndl. — Aside from its smaller size, the skull differs from that of 

 yosemite in the broader and more convex brain case, more widely 

 expanded zygomatic arches and reduction of ridges for attachment 

 of muscles. Occiput obliquely truncate permitting posterior portion 

 of condyles to be visible when skull is viewed from above. Dorsal 

 profile less uniformly convex, but ventral profile essentially^ the same 

 as in montanus. 



When viewed from above the brain case is somewhat rounded in 

 front, behind, and at the sides, seldom showing the square characters 

 of yosemite. Longitudinal ridges near outer edges of parietals becom- 

 ing more conspicuous with age, but not attaining that degree of 

 prominence which old individuals of yosemite exhibit. Interorbital 

 region narrow. Interorbital ridges distinct, with shallow median 

 sulcus, and closely approaching each other with age, until in old 

 individuals they coalesce. Interparietal as in montanus, its antero- 

 posterior diameter usually less and its lateral extremities more uni- 

 formly truncate. Frontals truncate or emarginate posteriorly. 



Compared with skulls of yosemite it has a proportionately shorter 

 and heavier rostrum, with least depth behind incisors greater than 

 width in same region, its proximal depth more than one-third greater 

 than least distal depth. Nasals short, narrowly spatulate, their 

 posterior terminations straight or slightly emarginate, and usuallj'^ 

 exceeded by ascending branches of premaxillae. Vertical depth of 

 anterior narial opening greater than transverse. Anteorbital foramen 

 variable in appearance, normally with superior breadth twice that 

 of inferior. Plate forming' outer wall, small and incomplete superiorly, 

 absent inf eriorly. 



Occipital view of brain case essentially the same as in yosemite, 

 the median depth equaling 58 per cent or more of the greatest width 

 across lambdoidal ridge of brain case. The foramen magnum is more 

 like that of typical montanus than yosemite.. Paroccipital processes 

 heavy, directed more downward than backward, their extremities for 

 the most part applied to bullae. Posterior margins of paroccipitals 

 continued upward on supraoccipital as in yosemite. Basioccipital with 

 prominent median ridge. Auditory bullae smaller and less globular 



