POCKET-MICE. 1 53 



the upper-parts is mouse-brown, becoming tawny on the flanks, while the under- 

 parts, the tip of the tail, and a spot above each eye are white or yellowish. In the 

 Rocky Mountains the place of this species is taken by Ord's kangaroo-rat ( D. ordi), 

 which is a rather larger and more stoutly built animal, with a relatively shorter 

 tail, and having five toes on each hind foot. 



The habits of the kangaroo-rats are very similar to those of the 

 jerboas, these Rodents frequenting the most arid districts they can 

 find, and living in burrows made beneath rocks or stones. In such districts there 

 is no water, and but little vegetation save gigantic cactuses ; and it appears that 

 the food of the kangaroo-rats is formed by the roots, blades, and seeds of the 

 scanty grass that manages to struggle into existence. Probably the only water 

 that these creatures drink is that derived from dew collected on the cactuses. 

 Little or nothing seems to be known of their breeding-habits. 



THE POCKET-MICE. 

 Genera Perognathus and Heteromys. 



The tiny little Rodents known in the United States as pocket-mice are dis- 

 tinguished from the kangaroo-rats by the presence of roots to their molar teeth, 

 and also by their inferior size the whole length of the head and body seldom 

 exceeding 2 inches. The genus Perognathus, as represented by the banded 

 pocket-mouse (P. fasciatus), of North America, is characterised by the hair being 

 coarse and bristly; whereas in the genus Heteromys, of which representatives 

 extend as far southwards as Trinidad, the fur is mingled with a number of 

 flattened spines. Most of these animals are brownish above and white beneath, 

 with a tawny stripe on the flanks dividing the dark from the light area. 



