1918] Kellogg: 3Iicwtus calif oniicus 'Group of Meadow Mice 23 



for anterior nares, with vertical diameter about equal to transverse. 

 Anteorbital foramen very variable in appearance ; in some individuals 

 narrow and high, with its superior portion scarcely if at all wider than 

 inferior ; in others superior width more than twice inferior width. The 

 plate forming outer wall and continuous with lacrimal bone internally, 

 almost complete superiorly, though absent inferiorly. 



Occiput evenly convex, the median depth averaging about 53% 

 of greatest width across lambdoidal ridge of brain-case. Foramen 

 magnum subtriangular, averaging smaller than that of aestuarinus. 

 Paroccipital processes heavy, directed downwards and slightly back- 

 wards, terminating rather bluntly. Their tips extend slightly if at 

 all behind most posterior point on supra-occipital above foramen 

 magnum. The posterior margins of paroccipitals are continued up- 

 wards as well marked ridges and usually unite with lambdoidal ridge 

 near outer extremities of interparietal. Basioccipital with poorly 

 defined median ridge. Auditory bullae large, but slightly smaller 

 than in aestuarinus, somewhat inflated, and otherwise essentially 

 similar. 



Palate with well marked palatine sulci, and slightly elevated median 

 ridge. Lateral bridges light, but well developed. Lateral pits of 

 palate distinct. Pterygoids and hamular processes rapidly diverging 

 posteriorly, and with posterior margin of palate notched. Interptery- 

 goid fossa somewhat narrower than in aestuarinus or calif or nicus. 

 Posterior palatine foramina almost obliterated. Incisive foramina 

 long, rounded at both ends and with greatest width in median portion. 



Central portions of zygomatic arches noticeably widened, and 

 maxillary roots heavier than in those of calif or nicus. Jugal enlarged 

 throughout and expanded anteriorly into a broad plate, which abuts 

 against maxillary root of zygoma. Zygomatic arches conspicuously 

 notched at anterior junction with premaxillae. 



Mandible robust, heavier than in mariposae. Ridges for masseteres 

 laterales strongly developed. Coronoid process light, its base slightly 

 wider than in mariposae, its extremity rising above level of condyle, 

 and curved backward. Angular process short and heavy, but curved 

 strongly outward. Periphery over base of incisor marked by an 

 obvious protuberance. Base of mandibular foramen decidedly above 

 level of cutting surface of last lower molar. Mental foramen on lateral 

 face situated somewhat below superior surface of diastema. 



Teeth. — In most respects the molariform teeth resemble those of 

 calif ornicus. Anterior loop of M^ crescentic. An internal lobe nor- 

 mally present on posterior triangle of M^. Long terminal loop of 

 M^ subtended externally by slight notch and internally by deep re- 

 entrant angle. Externoanteriorly this loop is decidedly crescentic 

 in outline. 



Mjwith anterior loop more deeply cut on internal side by reentrant 

 angle than on external side. Transverse loops relatively narrower 

 than transverse width of median portions of molars. 



Remarks. — So far as is known vallicola is separated from mari- 

 posae by the main ridge of the high Sierra Nevada. Collecting so far 

 has failed to show whether or not vallicola intergrades with kernensis 



