922 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
than the back. There is generally also a prominent whitish-yellow patch in 
front of the shoulders on the sides of the neck, where the hairs are also very 
coarse and stiff. 
In young specimens, the under fur is sometimes clear grayish-white, and 
the white tips of the overlying hairs are also longer than in the adults, with 
the subterminal zone darker. The rump, the sides of the neck, and a spot 
at the base of the ears are conspicuously pale yellowish-white. In several 
very young specimens (apparently but a few weeks old) from Colorado, the 
whole top of the head is intense black, and there is an abundance of soft under 
fur on the ventral surface. 
Arctomys flaviventer differs, as already noted, from A. monaz in its differ- 
ent coloration, larger size, smaller ears, and relatively much longer tail. Its 
much longer and much more heavily clothed tail affords at once a readily 
available distinctive characteristic. The coloration is also much more golden 
than in A. monax. The differences afforded by the skull have also already 
been detailed under that species. 
From A. pruinosus, it differs in its much smaller size, as well as in its 
totally different coloration, and in important cranial differences. A more 
detailed comparison will be given under A. pruinosus. 
Arctomys flaviventer was first described in 1841 by Audubon and Bach- 
man, from a specimen in the collection of the Zodlogical Society of London, 
brought by Douglass ‘‘from the mountains between Texas and California”. 
The habitat of this species extends from Western Texas, New Mexico, 
and Arizona northward throughout the Rocky Mountains to probably beyond 
the forty-ninth parallel. It occurs also in the Black Hills of Dakota, and 
specimens are in the collection from California. It is apparently a strictly 
alpine species. It is very abundant in the mountains of Colorado, occurring 
chiefly in the neighborhood of timber-line, and ranges to a considerable dis- 
tance above the forest vegetation, where it makes its home among the rocks. 
It is to some extent gregarious, like the A. marmota of Europe. 
