1922] Kellogg: Synopsis of Microius Mordax 285 



upperparts shades into light gray on face, sides and rump, the indi- 

 vidual hairs sometimes tipped with pinkish buff; forehead of same 

 color as dorsal stripe. Underparts whitish, dulled by the plumbeous 

 bases of hairs; anal area pure white. Whiskers pallid neutral gray 

 except short basal portions which are aniline black. Ears moderate in 

 size, with anterior border concealed by grayish hairs of face. Tail 

 distinctly bicolor, dusky drab or dark blackish brown above and 

 pallid neutral gray below, though when tail is scantily haired the yel- 

 lowish scales show through. Hands and feet covered with pallid mouse 

 gray hairs. In worn pelage : general coloration as a whole lighter. 



Skull. — Separable as a rule from that of sierrae by lighter and less 

 spreading zygomatic arches, the relatively shorter rostrum and smaller 

 bullae. Dorsal profile essentially the same. Occiput rounded, con- 

 cealing for the most part the condyles when skull is viewed from 

 above. All skulls examined, characterized by narrower brain case 

 than in sierrae, with sides rounded and rarely with postorbital tubero- 

 sities sufficiently developed to make any change in contour of the 

 skull. Longitudinal ridges poorly developed, continuous posteriorly 

 with lambdoidal ridge and anteriorlj^ with interorbital ridges. Inter- 

 orbital ridges variable in appearance, seldom prominent enough to 

 show a median sulcus. Interparietal with essentially same variations 

 as in sierrae. (See plate 8.) 



In superior view the slender rostral region tapers gradually toward 

 anterior end. Rostrum narrow, rarely wider at narrowest point behind 

 incisors than interorbital width, the least depth behind incisors greater 

 than width in same region. Nasals long, spatulate, widening at a 

 point anterior to middle, their posterior terminations emarginate. 

 Ascending arms of premaxillae exceeding the nasals and extending 

 to or beyond plane of lacrimals. Vertical diameter of opening for 

 anterior nares about equal to transverse. Anteorbital foramen narrow 

 and high, with superior portion considerably wider than inferior. 



Occiput not depressed or flattened, the median depth averaging 

 about 58 per cent of greatest width across lambdoidal ridge of brain 

 case. Outline of foramen magnum essentially as in sierrae. Par- 

 occipital processes usually directed more downward than backward 

 and applied to bullae at their extremities. Posterior margins of these 

 processes continued upwards on supra-occipital as sharp crests, termin- 

 ating below lambdoidal ridge. Basioccipital with well defined median 

 ridge. Auditory bullae smaller than in sierrae, flattened below meatus, 

 with their posterior margins indented by foramina. Palate slightly 

 narrower than in sierrae, with rather deep palatine sulci and elevated 

 median ridge. Lateral bridges light but well developed. Lateral pits 

 of palate exhibiting a variable amount of fenestration. Interpterygoid 

 fossa relatively narrow, the pterygoids and their hamular processes 

 gradually diverging posteriorly. Incisive foramina narrow, expanded 

 anterior to middle and equaling about 61 per cent of distance between 

 base of incisors and anterior borders of alveoli of first premolars. 

 Zygomatic arches diverging rapidly anteriorly, with region of greatest 

 convexity at junction of jugal with maxillary root of zygoma. Jugal 

 normally expanded, its head shallowl}^ mortised into maxillary root 

 of zygoma. 



