ia) 
HETEROMYID&, DIPODOMYINA. DIPODOMYS. 341 
derive their trivial name. They possess cheek pouches, and these, 
like those of the members of the GEomMyip#, are external, causing 
these families to differ from all other Mammals in this respect. 
These pouches are covered with hair on the inside as well as on the 
outside. The skull of these animals is peculiarly shaped and very 
light, being not thicker than a sheet of paper. The Kangaroo Rats 
are divided into two genera, one with four toes on the hind feet, 
the other with five; but in the latter the first digit, although possess- 
ing a claw, is rudimentary. These handsome little creatures live 
in burrows which they excavate in sandy soil, and they are preyed 
upon by the spotted skunks, which are numerous in the localities 
they frequent. They live in colonies and are very industrious, 
digging their burrows, some of which are several inches in diameter, 
in the shifting sand. They are hardy and do not seem to heed the 
severest weather, and run about on the snow when the thermometer 
registers below zero. At this time they feed on the seeds of cockle 
and sand burrs, and in summer on the seeds of the prickly pear and 
other hardy desert plants. They prefer the sandy districts near 
rivers, where vegetation is scanty, and on sandy portions of the 
prairies, and avoid those places where the soil is rich. They are 
nocturnal, passing the day in sleep, and their tracks in the sand 
each morning exhibit their activity and the extent of their night 
wanderings. They are exceedingly pretty creatures, with a pleasing 
coloring and fur as soft as silk, and with large, soft, expressive eyes. 
Fam. V. Heteromyide. Kangaroo Rats. Pocket Mice. 
Incisors narrow; molars rootless; mastoids enormously developed, 
appearing on top of the skull; hind feet long; digits four or five; 
pelage soft. 
Subfam. IV. Dipodomyine. 
Anterior molar without lobe to the prism. Skull two-thirds as 
wide as long, occipital plane emarginate; zygomatic plate of maxillary 
nearly roofing the orbit; pit on inner side of jaw near molars. 
41. Dipodomys. Four-toed Kangaroo Rats. 
l=; M.S= TO, 
Dipodomys Gray, Ann. Mag. Nat. Hist., v1, 1841, p. 521. Type 
Dipodomys phillipst Gray. 
Macrocolus Wagn., Archiv. fur Nattirg., 1846, I, p. 172. 
Skull light, depressed, smooth, thin, broad posteriorly, tapering 
anteriorly; anterior outline emarginate; rostrum extending beyond 
