HETEROMYIDjE 149 



salion in the quantity of weed seeds destroyed Tlie'r mouths 

 are small; the largest food I have known them to eat is acorns. 

 The family is digitigrade; nocturnal; terrestrial and sub- 

 terranean, living in burrows but gathering their food from 

 the surface. There is little if any seasonal change of pelage. 

 The sexes are alike, but the young sometimes differ from the 

 adults. 



Subfamily Dipodomyinae 



Skull triangular in general outline; molars rootless; tem- 

 poral region, enormously inflated; interparietal srnall, narrowed 

 from, the sides, sometimes obliterated; hind legs lengthened; size 

 comparatively large. 



Genus Perodipus Fitzinger. (Pouch — two-footed.) 

 Upper incisors grooved in front; temporal region greatly 

 inflated ; supraoccipetal, interparietal and parietals greatly reduced 

 in area; zygomatic arch expanded to a large thin plate in front 

 of the orbit; hind feet with five toes, the inner toe minute 

 and situated higher than usual; soles heavily haired; tail longer 

 than head and body, four striped ; eyes large ; ears large, rounded, 

 the front border inflexed ; pelage soft, without spines. 



The pattern of coloration of all the species of Perodipus and 

 Dipodomys is the same. There is a dark patch at the base 

 of the whiskers, a white spot over the eye, another below or 

 behind the ear, a white stripe across the thighs to the base of 

 the tail, a dark stripe on the upper side of the tail, usually another 

 on the under side leaving the sides of the tail white, fore feet 

 and all the lower parts from mouth to tail white to the roots of 

 the hairs. 



The beginner will find the species of Perodipus very puzzl- 

 ing, and will probably be unable to assign his specimens satis- 

 factorily. The division of this genus has been carried to an 

 unnecessary refinement. I have omitted several nominal species 

 or subspecies rather than add to the difficulty. Dipodomys is 

 not quite so difficult, as size and color are more diversified. 



