1922] Kellogg: Synopsis of Microtus Mordax 297 



length, 27.19 mm. (26.5-28) ; basilar length, Hensel, 23.82 mm. (22.8- 

 24.8) ; nasal length, 8.31 mm. (7.9-8.8) ; zygomatic width, 15.46 mm. 

 (14.9-16.1) ; interorbital constriction, 3.94 mm. (3.8-4.1) ; interparie- 

 tal width, 8.65 mm. (8.3-9) ; shelf of bony palate, 13.5 mm. (12.9- 

 14.6) ; height cranium at bullae, 9.85 mm. (9.7-10) ; mastoid width, 

 12.15 mm. (11.8-12.7) ; length upper molar series, 6.6 mm. (6.3-6.9) ; 

 length mandible, 16.48 mm. (16.1-17.3). 



Color. — General hue of dorsal area much darker than in sierrae, 

 the exact shade near snuff brown, but with an evident darkening; 

 middorsum usually overlaid with long aniline black overhairs. hi 

 fresh pelage : ground color of upperparts approaching bister but light 

 tipped hairs often as light as pinkish buff; basal portions of hairs 

 blackish plumbeous. Long overhairs ranging from mars brown to 

 aniline black. Color of upperparts shading into buffy on sides, and 

 this in turn giving way to pallid mouse gray. Underparts pallid 

 neutral gray, with varying admixture of white tipped hairs and with 

 faint suffusion of buff in the inguinal region; anal area nearly pure 

 white. Whiskers for the most part pallid neutral gray, with blackish 

 slate bases. Upper and lower lips white. Ears large, not concealed 

 by fur, with anterior border concealed by hairs of same color as those 

 of upperparts. Tail distinctlj^ bicolor, dull mars brown above and 

 pallid mouse gray below, though tail is often so scantily haired that 

 the 3^ellowish scales show through. Hands and feet covered with pale 

 drab gray hairs, occasionally with hairs as dark as light drab. In 

 worn pelage : much duller, lighter, and with an apparent reduction 

 in amount of long overhairs on upperparts. Young : coloration of 

 upperparts of young individuals very dark as compared with adults 

 because of preponderance of aniline black overhairs, though there is 

 a slight suffusion of buff.y on sides and on head. Inunature individuals 

 are characterized hy the increase in amount of light tipped hairs, and 

 by the increased size of the grayish patch' on each side of the body. 



Skull. — In all general features the skull agrees with that of sierrae, 

 but brain case is relatively smaller, narrower, and not so convex 

 dorsally. Occiput not abruptly truncate, though occipital condyles 

 are barely visible when skull is viewed from above. (See plate 8.) 



This race has a rather long and narrow brain case, slightly rounded 

 at the sides. Postorbital tuberosities usually small, producing no con- 

 spicuous change in contour of skull. Longitudinal ridges along outer 

 edges of parietals well indicated anteriorly, but tending to disappear 

 posteriorly. Interorbital region resembling that of niordax; inter- 

 orbital ridges variable, normally indistinct in interorbital region and 

 with median sulcus very shallow if present. Interparietal similar to 

 that of mordax, but with posterior margin biconvex and lateral extrem- 

 ities less obliquely truncate ; its anteroposterior width, exclusive of 

 median projection, equal to one-third or more of its greatest trans- 

 verse diameter. Frontals normally broadly concave posteriorly. 



The proximal width of rostrum slightly greater than in sierrae. 

 Nasals extending forward to or beyond front plane of incisors and 

 posteriorly not quite so far as ends of ascending branches of pre- 

 maxillaries. Lateral borders of nasals, when viewed from above, 

 essentially straight with slight constriction anterior to middle. An- 

 terior narial opening, with vertical diameter about equal to transverse. 



