1914] Grinnell: Mammals and Birds of the Colorado Valley 



93 



deserti may be cited. This rodent, taking its entire, irregular and 

 discontinuous range into consideration, is closely restricted to those 

 portions of the desert affording a deep surface layer of fine sand. 

 Areas of aeolian sands constitute its typical home territory (see pi. 11, 

 fig. 16). Now, it is quite probably not any peculiarity of food-supply 



Fig. D. Diagram showing frequency of capture of Perognathus p. penicil- 

 latus in the several associations. Two hundred and seventeen individuals were 

 taken, of which associational occurrence was definitely recorded. This species 

 is seen to be very widely distributed, yet exhibiting marked preference for 

 certain associations. 



attaching to the aeolian sands, which binds the animal to them in this 

 case rather than to the mesa at large ; but it is the animal 's require- 

 ments in the way of retreats for diurnal safety and for breeding. 

 These, by nature of its fossorial limitations, Dipodomys d. deserti is 

 unable to construct for itself except in ground easy to burrow into to 

 a depth commensurate with its own large size and in soil with a 

 proper degree of coherence. 



