GEOMYID^ 135 



not cowardly. They seem to fear nothing and will attack any- 

 thing that molests them. 



Being subterranean in habit, working in the dark, they are 

 active at all hours, but are least so in the middle of the day. In 

 soft earth the digging is done with the fore feet, but in hard 

 soil the incisors are used tO' loosen it. As the earth is loosened 

 it is scratched back to the hind feet which pass it on until enough 

 for a load is ready, when the animal turns around, brings the 

 wrists together under the chin, the fore feet extended out- 

 ward, and then, propelled only by the hind feet, the dirt is pushed 

 ahead of the animal to the outer opening of the burrow, when 

 the dirt is thrown out by a quick flirt. They run "backward 

 nearly as rapidly and easily as forward, the sensitive tip of the 

 tail being used as a guide. 



The pelage of the adult is commonly somewhat different 

 from that of the young, and in some species there is also seasonal 

 changes. They breed pretty much throughout the year or 

 through the warm months in the colder part of their habitat, 

 but it is not known whether the females breed more than once 

 a year. The young are born in an undeveloped condition. Two 

 to six constitute a litter. 



Genus Thomomys Maximilian. (Heap — mouse.) 

 Front surface of incisor without a longitudinal groove, or 

 but a small one very near the inner edge; upper and lower molars 

 with two enamel plates, one anterior, one posterior ; external ears 

 evident though small ; four pairs of mammae in most species. 



Dental forrnula, I, i — i ; C, o — o; P, i— i ; M, 3 — 3X2=20. 



Thomomys fulvus nigricans Rhoads. (Fulvous; 

 blackish. ) 



TAWNEY POCKET-GOPHER. 



Variable in color ; above usually yellowish bistre mixed with 

 black dorsally from crown to hips ; sides lighter ; below grayish 



