642 



MILLER 



ters). Skull narrower than that of A. univlttatus^ the dorsal profile 

 essentially straight from tip of nasals to middle of proencephalon. 



Piir. — The fur is rather coarse and harsh, but without bristles or no- 

 ticeable lengthened hairs. On middle of back it is about 8 mm. in length. 

 Color. — Face, cheeks, back, and sides uniform dull orange-rufous, 

 slightly darkened by a uniform admixture of black-tipped hairs; these 

 a little less noticeable on sides. A black line, 3 mm. wide, extends 

 from nape to rump. Ventral surface buff (slightly yellower than 

 Rido-way, p1. v, no. 13), fading to dirty white on throat, chin, lips, 

 and inner side of front legs, and deepening to ochraceous in anal region 

 and on inner side of hind legs. Hind feet thinly coated with short 

 ochraceous hairs. Front feet dull brown. Tail and ears uniform 

 dark brown. 



Peet. — The feet present no characters of importance. Soles with 

 five well-developed tubercles and apparently a rudimentary sixth. 

 Palms 6-tuberculate. Thumb very small, its nail blunt. 



Tail. — The tail is moderately long and rather thick, its annulation 

 distinct. At middle there are 15 rings to the centimeter. The indi- 

 vidual rings are somewhat irregular in outline at free border, but are 

 not distinctly broken up into scales as in Mus tullbe7-gi. From be- 

 tween the rings spring numerovis black stiff hairs, the length of which 

 is slightly greater than width of rings. Toward tip the rings become 

 confused and crowded, but the hairs undergo no change. 



Skull. — The skull of Arvicanthis plani- 

 frons (fig. 41) differs fromthat of A. tint' 

 vittatus in many important characters. In 

 general it is more slender than the latter, 

 though the ridges are equally well devel- 

 oped. The most striking peculiarities are 

 to be found in the anterior half of the skull. 

 The whole region in front of the interorbital 

 constriction is reduced in both width and 

 depth, and as this lessening most affects the 

 region between anterior bases of zygomata a 

 conspicuous change in the profile of the 

 skull results. In A. luiivittattis the dorsal 

 outline curves almost continuously (though 

 it is nearly straight over front half of nasals) 

 from front to back, the convexity slightly 

 more abrupt at front of orbits and over mesencephalon. In A. plani- 

 frons it is essentially straight from anterior extremity of nasals to 



Fig. 41. a Arvicanthis 

 planifrons ; b A. nnivilia- 

 tus. Slightly reduced. 



