298 University of California Publications in Zoology [Vol. 21 



Aiiteorbital foramen essentially as in sicrrae, though in some cases 

 slightly broader, with inferior termination more angular and less 

 rounded. 



Outline and depth of occiput when viewed from behind, similar 

 to that of sierrae, the median depth equalling about 56 per cent of 

 gTeatest width across lambdoidal ridge of brain case. Foramen 

 magnum essentially the same as in sierrae. Paroccipital processes 

 applied to bullae, their posterior margins continued upward as crests 

 which usually terminate below lambdoidal ridge. Median ridge of 

 basioccipital poorly defined. Auditory bullae usually smaller than 

 those of sierrae, their posterior boundaries slightly indented by fora- 

 mina. 



Palate similar in many respects to that of sierrae. Palatine sulci 

 well indicated, but with narrow median ridge. Lateral bridges light, 

 walls of lateral pits somewhat fenestrated and pterygoids and hamular 

 processes nearly parallel. Posterior margin of palate usually concave. 

 Interpterj^goid fossa slightl}^ narrower than in sierrae. Posterior pala- 

 tine foramina wide open. Incisive foramina wide open, much more 

 so than in other members of this group, with widest portion usually 

 anterior to middle. 



Zygomatic arches divergent anteriorly, the maxillarj^ root strongly 

 curved backward. Jugal relatively heavy, essentially as in sierrae, 

 though usually broader. Zygomatic arches slightly notched at anterior 

 junction with premaxillaries. 



Mandible light, with relatively deeper horizontal ramus than in 

 sierrae. Ridge for masseteres laterales very well developed. Coronoid 

 process small, short, its extremity not rising above level of condyle, 

 and curved but little backward. Angular process relatively narrow, 

 attenuate, but not curved stronglj^ outward. The articular tuberosity 

 over base of incisor prominent, but included in masseteric ridge, and 

 not lying for the most part above as in other races of this group. 

 Mandibular and mental foramina the same as in sierrae. 



Teeth. — Except for their greater size, a character noticeable in 

 both the incisors and molariform series, the teeth do not differ appre- 

 ciably from those of Microtus niordax sierrae. The metacone may 

 (figs. Z and AA) or may not (fig. BB) be closed inferiorly; hypocone 

 may fuse with metacone (fig. Z). No incipient internal reentrant 

 angle was found on terminal loop of M^ in any of tlie specimens 

 examined. 



Remarks. — It is of peculiar interest to note the existence of this 

 race in the remote San Bernardino Mountain area. It is probable 

 that the mordax group at one time had a much wider distribution 

 within the state than at present, and there is little reason to doubt 

 that it formerly had continuous distribution from the southern Sierra 

 Nevada to the mountains of southern California, and that geological 

 changes have resulted in the isolation of this form within its present 

 limited habitat. Another point of interest is offered in the bearing 

 of the distribution of Microtus califormciis neglectns, which extends 



