270 U)iiversity of California Publications in Zoology [Vol. 21 



than in yosemite, with the posterior borders slightly indented by 

 foramina in bullae. 



Palate wide, with palatine sulci distinct. Median ridge narrow, 

 and lateral bridges light. Lateral pits of palate with variable fen- 

 estration, usually deeper than in yosemite. Pterygoids and hamular 

 processes abruptly diverging posteriorly. Interpterygoid fossa nar- 

 row. Postpalatal border may be evenly concave, or present a slight 

 median process. Posterior palatine foramina distinct. Incisive fora- 

 mina narrow, equalling about 60 per cent of distance between base 

 of incisors and anterior border of alveolus of first premolar. Zygo- 

 matic arches widely spreading, expanded at middle and relatively 

 heavy, with rather broad maxillary root. The jugal is very broad, 

 its head strongly embedded in maxillary root of zygoma, but averaging 

 shorter than in yosemite. 



Mandible light and slender, more so than in yosemite, approaching 

 montanvs more closely in proportions. Relative depth of horizontal 

 ramus shallower than in the former. Ridge for masseteres laterales 

 essentiall.y as in montanns. Coronoid process long, slender, its base 

 narrow, its extremity rising above level of the condyle and normally 

 curved strongly backward. Angular process rather wide at base, 

 terminating bluntlj^ and curving more strongly outward than in nion- 

 tanus. Articular process over base of incisor not marked by a prom- 

 inent tuberosity. Base of mandibular foramen normally on a level 

 with cutting surface of last lower molar. Mental foramen situated 

 on lateral face below superior surface of diastema, as in yosemite. 



Teeth. — In general the teeth are like those of yosemite, but with 

 deeper transverse loops. The enamel folding of the terminal loop 

 of M- (figs. U to X) may frequently be of a more complicated type 

 than in either tnontanus or yosemite. In this case the enamel posteriad 

 to the metastyle of the long terminal loop forms an angle with its 

 anterior continuation (fig. V). Enamel section enclosing metacone 

 variable in outline, normally closed inferiorly. The long terminal loop 

 is normally not subtended externally, just posterior to the metacone, 

 by indentation of enamel. Lower molariform series not exhibiting 

 any marked peculiarities other than a very variable fourth premolar. 



Remarks. — The writer disagrees with Bailey's statement (1900, 

 p. 33) that "the two species [i.e., montamis (^yosemite) and 

 d'utcheri] occupy widelj^ separated zones and show no evidence of 

 intergradation. " As regards zones both races are present in the 

 Canadian and both range up into the Hudsonian. Microtus montanvs 

 yosemite has been collected in the Transition zone also. Certain of 

 the specimens listed by Bailey {loc. cit.) as dutcheri prove upon 

 reexamination to be referable to yosemite; these were collected at 

 Mammoth, Pine City, and near the head of the San Joaquin River, 

 localities considerably north of the Kearsarge Pass (see map). 



In the writer's estimation neither the quality of the characters 

 exhibited by dutcheri nor the degree of difference in these characters 

 as compared with those of yosemite are of sufficient importance to 



