352 HETEROMYINZ. 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 Dipodomyine, 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. Heteromyine. 
C. H. Merriam. Revision of the North American Pocket Mice, 
N. Am. Faune ease, 1830. 
W. H. Osgood. Revision of the Pocket Mice of the genus Perog- 
nathus, N. Am. Faun., No. 18, 1900. 
73. Perognathus. Pocket Mice. 
CS Pp Me = 20. 
SY te 38 
Perognathus Wied. Nov. Act. Phys. Med. Acad. Caes. Leop. 
Carol., xIx, 1839, pp. 368-373, pl. xxx1v. Type Perog- 
nathus fasciatus Wied. 
Cricetodipus Peale, Rep. Mamm. & Ornith. U. S. Expl. Exped., 
1848,"p. 53, ple ma, ie. 
Abromys (sic) Gray, Proc. Zo6l. Soc., 1868, p. 202. 
Otognosis Coues, Proc. Acad. Nat. Scien. Phil., 1875, p. 305. 
Chetodipus Merr., N. Am. Faun., No. 1, 1889, p. 5, pl. 11, fig. 15. 
Skull depressed and flat above; nasals lengthened, projecting 
beyond incisors; mastoids less developed than those of the species 
of Dipidomyine, 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. 
