922 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 



than the back. There is generally also a prominent whitish -yellow patch in 

 Iron! of the shoulders on the sides of the neck, where the hairs arc also very 

 coarse and stiff. 



In young specimens, the under fur is sometimes clear grayish-white, ami 

 the white lips 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 jiaviventer differs, as already noted, from A. monax 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 Jlaviventer was first described in 1841 by Audubon and Bach- 

 man, from a specimen in the collection of the Zoological 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. 



