SCIURID.E— ARCTOMYS PRUINOSUS. 925 



black; below clear whitish-gray. A small occipital area and tlie feet black 

 Head anteriorly, with the sides of the muzzle and the chin, white or grayish- 

 white, and the top of the nose generally black. Ears quite small, well 

 clothed, and nearly concealed by the surrounding pelage. Tail full and round, 

 with the hairs rather less than one-half of the length of the head and body. 

 The hairs are yellowish-white externally, slightly varied with black, and 

 dark reddish-brown basally. 



Different specimens vary in the amount of black mixed with the gray 

 and in the intensity of the fulvous suffusion posteriorly. The anterior two- 

 thirds of the dorsal surface is often nearly white, with a slight admixture of 

 black-tipped hairs ; at other times, the black and white are present in nearly 

 equal proportions, while again the black predominates. The posterior third 

 of the dorsal surface, together with the tail, is generally more or less suffused 

 with pale whitish-fulvous, sometimes varying to deep fulvous. The pelage 

 is very soft and full, and the under fur very abundant and long. Anteriorly 

 it is brownish-black at base, and clear white apically, or with a slight tinge 

 of yellowish ; posteriorly the basal zone is more strongly brownish, with the 

 apical zone pale whitish -yellow. Many of the longer overlying hairs are 

 wholly clear white; others are colored basally like the under fur, with the 

 tips pure black. The lower surface is rather thinly haired, with, however, 

 more or less under fur. The hairs are mostly pure white to the base: the 

 scanty under fur is brownish, and shows to a greater or less extent through 

 the surface hairs, giving a dingy brownish-white appearance to the ventral 

 surface. Some of the long hairs are wholly black, and others are black- 

 tipped. Occasionally the ventral surface is quite strongly tinged with rufous. 

 In a half-grown specimen, the ventral surface is much more thickly clothed 

 than in the adults. 



One specimen from Fort Yukon (collector's No. 258) has the hinder 

 part of the back spotted with black and dark chestnut, arranged in large 

 irregular patches. In this specimen, the whole upper surface of the head is 

 black, mixed slightly with gray; the nose and the edge of the chin are also 

 black. The muzzle and chin are usually white, and the top of the head 

 black, but the black area is of irregular outline and of variable extent. The 

 white area on the nose is sometimes very restricted, and again extends posteri- 

 orly to a point opposite the eyes, extending back laterally so as to form a 

 broad band over each eye ; in other specimens, the black area reaches later- 



