1^22 J Kellogg: Synopsis of Microtus Mordax 295 



lateral bridges. Lateral pits of palate variable, usually with distinct 

 fenestration. Pterygoids and hanmlar processes slightly diverging 

 posteriorly. Posterior margin of palate usually concave, sometimes 

 notched. Interpterygoid fossa averaging a little narrower than in 

 typical mordax. Posterior palatine foramina open. Incisive fora- 

 mina narrow, somewhat constricted at ends, and equal to about 62 

 per cent of distance between base of incisors and anterior border of 

 alveoli of molariform series. 



Zygomatic arches light, broadly spreading posteriorly, expanded 

 at the middle and narrowing anteriorly. Z.ygomatic arches deeply 

 notched at anterior junction with premaxillaries. Jugal heavier, 

 deeper and more firmly mortised into zygoma than in mordax. 



Mandible small, relatively short and deep. Inferior border of 

 ramus nearly straight, forming a more abrupt angle with chin than 

 in califor)dcus. Ridge for masseteres laterales well developed and 

 but seldom as sharp as that exhibited by mordax. Coronoid process 

 very slender, its extremity rising to or slightly above level of condyle, 

 and curved strongly backward at tip. Condylar process slender and 

 long, much more so than in typical mordax or calif or nicus. Angular 

 process well developed but not narrowing abruptlj^ near extremity 

 and curved but little outward. Surface of mandible over base of 

 incisor not marked by such an obvious protuberance as in mordax. 

 Mandibular and mental foramina essentially as in mordax. 



Teeth. — AVliile in no way essentially different from the average 

 of those of Microtus mordax mordax, the teeth of ill. m. angusticeps 

 appear to be more uniform in the enamel folding of the crown. The 

 metacone of M^ may (figs. U. V, and X) or may not (figs. W and Y) 

 be open inferiorly ; the internal reentrant angle on terminal loop may 

 be rudimentary (fig. X), or may be conspicuously developed (fig. V) ; 

 an incipient secondary internal reentrant angle may be present on 

 terminal loop (fig. W). 



Remarks. — Microtus mordax angusticeps is a depauperate form 

 of the mordax group, with a notably restricted range, being known 

 at present only from a narrow coastal strip of northern California 

 lying between Point St. George and Cape Mendocino. It is most com- 

 monly met with in marshes or in damp redwood forests a few feet 

 above sea level. It is an apparently isolated offshoot, probably pre- 

 vented from free interbreeding with sierras, with consequent little or 

 no chance for geographic intergradation, hj some disadvantageous 

 intervening condition of territory. 



Angusticeps resembles both sicrrac and mordax in many respects, 

 though certain external characters make it difficult to decide which 

 should be considered the immediate parent stock. In the vicinity of 

 Eureka and Crescent City, individuals of large size have been col- 

 lected which are unquestionably referable to the mordux group. As 

 regards cranial characters, it will be noted that the skulls are larger 

 and more angular, yet the outlines of the incisive foramina resemble 



