GEOMYID/t. :MI 



level, in the same manner as is witnessed in the case of moles. So 

 completely do they live in the ground that one is rarely seen upon it. 

 These animals are provided with cheek pouches, some of enormous 

 size reaching even to the shoulders, and these are convenient recep- 

 tacles for food and afford a means for transporting it from place to 

 place. In some localities Gophers are veritable pests, undermining 

 the soil with their endless galleries, and flinging the earth excavated 

 from these burrows on every side. In size these animals vary con- 

 siderably, some being as large as a full grown rat, and others again 

 not half that bigness. The pelage is exceedingly soft, even silky. 

 The skull is heavy, its muscles large and powerful, and the cutting 

 teeth strong and effective, adze-shaped. The family is divided into 

 two chief genera, Geomys and Thomomys, distinguished by the 

 presence or absence of median grooves on the incisors. 



Pam. IV. dreomyidfe. Pouched Rats. 



C. H. Merriam, Monographic Revision of the Pocket Gophers, N. 

 Am. Faun., No. 8, 1895. 



Large, fur-lined cheek pouches present, opening outside the mouth. 

 Squamosals expanded ; jugal extending to lachrymal; palate sloping 

 below level of zygomata, which are strong and flaring; molars rootless; 

 lower jaw strong; form arvicoline; fore feet fossorial; eyes and ears 

 minute. 



KEY TO THE GENERA. 



A. Skull large, flat, rather massive; upper inci- 

 sors grooved; jugal extending to lachrymal; 

 mandible powerful, 

 a. Upper premolar with three enamel plates, the 



posterior absent. PAGE 



a.' Upper incisor bisulcate Geomys 310 



b.' Upper incisor unisulcate. 



a." First and second upper molars with one 



enamel plate each, posterior absent, 

 a/" Squamosals not greatly expanded 

 laterally; orbitosphenoids articulat- 

 ing anteriorly with alisphenoids Cratogcomys 311 



b/" Squamosals greatly expanded later- 

 ally; orbitosphenoids not articulat- 

 ing anteriorly with alisphenoids Platygcomys 3 1 6 



b." First and second upper molars with two 

 enamel plates each. 



