352 HETEROMYINJE. PEROGNATHUS. 



The Pocket Mice, while related to the Kangaroo Rats, have not 

 their long hind limbs; indeed, these members scarcely exceed the 

 fore legs in length, and the pelage, instead of being soft and silky, 

 is usually harsh and coarse. The skull, however, is of a papery 

 construction, and the tail is long, and often tufted, and the general 

 appearance of the animals, especially in some of the species, is not 

 unlike that of the Kangaroo Rats. The cheek pouches have rather 

 narrow openings, but extend back nearly to the ears. The Pocket 

 Mice differ somewhat in their habits from the Dipodomyince , and 

 apparently hibernate, for they are rarely seen during the winter in 

 localities where the temperature goes below zero. They are prairie 

 dwellers, and make their burrows amid the buffalo grass, sinking 

 them perpendicularly for five or six inches, and the excavated earth 

 is piled up in little mounds near the opening. These mice are gen- 

 erally small in size, some species being indeed almost minute. They 

 are divided into two subgenera, distinguished from each other by 

 variations in the skulls. 



Subfam. V. Heteromyinse. 



C. H. Merriam. Revision of the North American Pocket Mice, 

 N. Am. Faun., No. i, 1889. 



W. H. Osgood. Revision of the Pocket Mice of the genus Perog- 

 nathus, N. Am. Faun., No. 18, 1900. 



73. Perogiiatlms. Pocket Mice. 



Perognathus Wied. Nov. Act. Phys. Med. Acad. Caes. Leop. 



Carol., xix, 1839, pp. 368-373, pi. xxxiv. Type Perog- 



nathus fasciatus Wied. 

 Cricetodipus Peale, Rep. Mamm. & Ornith. U. S. Expl. Exped., 



1848, p. 53, pi. 13, fig. 2. 



Abromys (sic) Gray, Proc. Zool. Soc., 1868, p. 202. 

 Otognosis Coues, Proc. Acad. Nat. Scien. Phil., 1875, p. 305. 

 Chcetodipus Merr., N. Am. Faun., No. i, 1889, p. 5, pi. in, fig. 15. 



Skull depressed and flat above; nasals lengthened, projecting 

 beyond incisors; mastoids less developed than those of the species 

 of Dipidomyina, and in certain species not projecting beyond plane 

 of occiput; zygomata much as in ordinary rodents; occiput not 

 emarginate; molars rooted; no pit between last lower molar and 

 coronoid process; tail moderate; soles naked or sparsely haired; hind 

 limbs scarcely exceeding the fore limbs in length. 



