SCIURIDAX—ARCTOMYS PRUINOSUS. 925 
black ; below clear whitish-gray. A small occipital area and the 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 toa 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 forma 
broad band over each eye; in other specimens, the black area reaches later- 
