16 



NOETH AMERICAN FAUNA, 



[no. 39. 



in carrying earth from the burrows, but such is not the case as, in pre- 

 parmg many hundreds of specimens, I have never found earth in the 

 pockets, except for minute particles from roots and bulbs. Other 

 naturalists have given the same negative evidence. On the other hand, 

 the pockets are commonly stuffed full of vegetation. I have often 

 watched the gopher come to the surface, opening a new doorway as he 

 came, and begin to draw down one plant after another, cutting and 

 tucking away the sections in his pockets as he drew them down. His 

 motions are quick as a flash, and that the hands are used in filling the 

 pockets is about all one can be sure of. Dr. Merriam found by watch- 

 ing a captive specimen of Geomys that the hands were used for both 

 filling and emptying the pockets.* 



CRANIAL CHARACTERS. 



In Dr. Merriam's very full discussion of the morphology of the 

 skull in his Monographic Revision of the Geomyidse ^ numerous figures 

 and illustrations of the genus Thomomys are included. In the present 

 work it is therefore necessary only to mention some of the variations 

 and general characters useful in the separation of the various forms. 



In aU, the cranium is wide and low, with spreaduig zygomatic arches 

 for the accommodation of powerful muscles. The mandibles are heavy 

 and u*regular, and the incisors above and below are long, curved, deeply 

 embedded tools of labor and weapons of defense. The relative length 

 and breadth of the skuU vary greatly in different species: shortening 

 of the total length generally implies a relatively wider skull; elongation 

 a relatively narrower. In some species, however, the rostrum alone is 

 elongated or shortened, in others the braincase varies in length and 

 breadth. The generally wedge-shaped nasals are extremely variable 

 in length and form, especially in form of termination at posterior tips. 

 The premaxillae in some terminate even with the posterior line of the 

 nasals, in others they extend weU back into the frontals with pointed, 

 beveled, or truncate tips. 



The interparietal furnishes a convenient character for the recogni- 

 tion of many forms, varying from a minute oval to a large quadrate 

 bone covering nearly half the basal width of the skull. In some 

 species, however, it is obscured in old age until completely obliterated 

 in a high sagittal crest, in others advanced age produces no appre- 

 ciable change. The various forms of the line of junction between the 

 base of the zygomatic processes of the maxillas and the premaxillse and 

 frontal and lachrymal bones furnish excellent specific as well as group 

 characters. In the umhrinus group the bases of these bones are forked 

 or concave; in most others convex, straight, or doubly curved. There 

 are often good characters in the symphysis of the z3^gomatic process 



1 N. Am. Fauna No. 8, 18, 1895. 



2 Ibid., 33 and 198, 1895. 



