1922] Kellogg: Calif ornian Forms of Microtus Montmvus 267 



ridges than in nwntanus. Basioccipital with distinct median ridge. 

 Bullae large, rounded, with posterior margins less obliquely truncated 

 and with region anterior to and below meatus flattened or depressed. 



Palate about equal in width to that of montmiiis. Palatine sulci 

 apparently deeper, with more distinct median ridge. Lateral bridges 

 light, and with lateral pits of palate exhibiting a variable degree of 

 fenestration. Pterygoids and hamular processes abruptly diverging 

 posteriorly. Interptcrygoid fossa relatively narrow, with posterior 

 margin of palate normally notched. Posterior palatine foramina large 

 and distinct. Incisive foramina equaling about 63 per cent of distance 

 between base of incisors and anterior border of alveoli of first pre- 

 molar. Zygomata broadly spreading, with median portion, except 

 in very old individuals, parallel with main axis of skull, and notched 

 at junction with premaxillae. Jugal similar to that of montanus, but 

 broader and more deeply mortised into maxillary root of zygoma. 



Mandible relatively longer, heavier, and deeper throughout than 

 in montanus. Ridge for masseteres laterales prominent. Coronoid 

 process large ; its extremitj^ may or may not rise above level of condjde, 

 with posterior curvature of tip variable. Angular process similar to 

 that of rmmtan'ns, but usually with more pointed tip. Articular 

 process over base of incisor marked by a large protuberance. Man- 

 dibular and mental foramina situated in same position as in montamis. 



Teeth. — Not differing appreciably from those of montanus, though 

 molariform series averages smaller. Enamel folding of M- (figs. Q 

 to T) without any special peculiarity except that the anterior loop 

 is normally evenly convex, the enamel section enclosing the metacone 

 is seldom open inferiorly, and the long terminal loop is usually more 

 crescentic than in montanus. 



Lower molariform series (fig. A) similar to that in montanus. 



BemarJis. — This gray colored race of meadow mouse inhabits the 

 Sierra Nevada region north from the headwaters of the San Joaquin 

 River, and ranges beyond the limits of California into Oregon and 

 Nevada in the Great Basin region. Using cranial characters as a basis 

 it was found that specimens from the northeastern part of the state 

 resemble topotypes of yosemite more closely than nvontanus. 



In this subspecies the majority of the specimens are lighter in 

 tone of color than those of typical montanus, though there are many 

 that can with difficulty be distinguished either from montanus or from 

 dutcheri. Specimens from Modoc County are not exactly like those 

 from Yosemite Valley, nor are those from Placer and Nevada counties 

 exactly like those from Modoc County or Yosemite Valley, though all 

 these localities lie within what is here considered to be the range of 

 yosemite. Occasional specimens from the western side of Owens 

 Valley exhibit the buffy underparts which are characteristic of 

 dutcheri, but their other characters clearly place them within the race 

 yosemite. 



