OF DENISON UNIVERSITY. 1 9 



Being practically subterranean they are little exposed to interrup- 

 tion and from their habits little likely to spread rapidly, they multiply 

 in favorable localities to an incredible extent and miles of meadow 

 land are honey-combed by their burrows. Their natural habitat is 

 moist sandy bottom or prairie land where vegetation is succulent and 

 the soil yielding. A large river naturally forms an almost insuperable 

 barrier to their distribution. The centre for the whole group is in the 

 upper Missouri region and various species extend northward into the 

 Saskatchewan region and southward into Mexico. The group does 

 not extend much east of the Mississippi except in the Gulf States. 

 The existing genera are closely related. In New England and the 

 Middle States they are entirely absent. There are obvious resem- 

 blances in the various members of the Gcomyidw to the field mice 

 ArvicolincB especially in important cranial characters while a more super- 

 ficial resemblance, due chiefly to the presence of cheek pouches, allies 

 them with the pouched mice or SaccomyidcB. There are many points 

 of agreement also with the African mole rats (Georychida) which they 

 more nearly resemble in their habits. 



As just indicated, these low-bodied, rat-like, but densely furred 

 animals are chiefly remarkable for the large tur-lined pockets extend- 

 ing from the shoulder to the sides of the mouth but opening entirely 

 outside the buccal cavity. These pouches have special muscles and 

 are used in carrying food which, in all the species, is stored in subter- 

 ranean graneries. 



The fur is dense and very soft and mole-like. The under fur is 

 plumbeous and very fine. Superficially the color is a subdued but 

 rich brown with a purplish or reddish reflection and a glossy bril- 

 liancy during life which is lost in the prepared skin. The head and 

 middle of the back are darker brown. • Beneath, the colors are much 

 lighter becoming whitish on the feet, tail and lower lip. There is also 

 a light spot on the nose and below the small muffle. The vibrissa 

 are thin and pale. The female is lighter. A peculiar phase of color- 

 ation not known to correspond to any seasonal or physiological condi- 

 tion, occurs in animals which are dark gray, almost black, and uniform 

 throughout. In old individuals there is a considerable admixture of 

 white hairs especially upon the head. In summer the feet and tail 

 become nearly naked. In form the pocket gopher differs form the 

 rat-like rodents in the large relative size of the head and shoulders as 

 well as the fore fed. The body tapers rapidly backward and the hind 



