168 CALIFORNIA MAMMALS. 



Perognathus penicillatus Woodhouse;. (Pencil like.) 



TUFT-TAILED POCKET-MOUSE. 



Above pale day color or vinaceous buff, sparsely intermixed 

 with blackish hairs; below white; lateral line obsolete; hairs of 

 terminal third of tail lengthened, forming a distinct "pencil" at 

 tip; tail similar to back above, darkening toward tip, white below; 

 soles naked ; no spines on the rump, but sometimes small bristles 

 are present ; skull comparatively narrow ; mastoids small ; inter- 

 parietal rather large, the angles rounded, transverse breadth near- 

 ly twice the longitudinal ; interorbital region wide. 



Length about 200 mm. (8 inches) ; tail vertebrae 109 

 (4.70) ; hind foot 25 ( i ) . 



Type locality, near San Francisco Mountain, Arizona. 



This Pocket-Mouse is rare in the region where it was first 

 found, that being in the edge of its habitat. It is more common 

 along the Colorado River, but is not typical in the lower part of 

 that region, gradually blending intO' the next subspecies. 



Perognathus penicillatus angustirostris Osgood. (Nar- 

 row — rostrum. ) 



COLORADO DESERT POCKET-MOUSE. 



Similar to penicillatus; averaging smaller; rostrum longer 

 and more slender; color similar. 



Type locality, Carrizo Creek, southwestern border of the 

 Colorado Desert. 



This Pocket-Mouse is common throughout the Colorado 

 Desert, the southeastern part of the Mojave Desert, the southwest- 

 ern corner of Arizona, northwestern Sonora and northeastern 

 Lower California. The relative abundance is determined by the 

 abundance or scarcity of plants and therefore of food. In con- 

 siderable barren areas they are practically lacking, and in a few 

 favorable localities they are abundant. I remember catching 

 twenty-seven one night in a thick patch of weeds. Their food 

 is mostly the small seeds of plants; mesquit beans are eaten to 



