ftx'?Sta } LIFE HISTORY OF THE KANGAROO RAT. 5 



Key to Species of Dipodomys in Arizona. 



a\ Size much larger (hind foot and greatest length of slcull more than 42 

 millimeters) ; tail tipped with white. 



&\ Upper parts dark brownish buffy ; tail dark brownish or blackish 

 with more sharply contrasted white tip; interparietal broader, 

 distinctly separating mastoids (range in Arizona mainly south- 

 eastern part) Dipodomys spectabilis. 



tt.^ Upper parts light ochraceous-buffy ; tail pale brownish with less 

 sharply contrasted white tip ; interparietal narrower, reduced to 

 mere spicule between mastoids (range in Arizona mainly south- 

 western part) Dipodomys deserti, 



a^ Size much smaller (hind foot and greatest length of skull less than 

 42 millimeters) ; tail not tipped with white. 



l)\ Hind foot with four toes Dipodomys merriami. 



h\ Hind foot with five toes Dipodomys ordii. 



On account of the small size, merHami and ordii do not require 

 detailed color comparison with the other two. The general color of 

 the upperparts of spectahilis is much darker than that of deserti; 

 whereas spectabilis is ochraceous-buff or light ochraceous-buff griz- 

 zled with blackish, deserti is near pale ochraceous-buff and lacks the 

 blackish. 



The color of the upperparts alone amply suffices to distinguish 

 spectahilis and deserti; but the different coloration of the tail is the 

 most obvious diagnostic feature. The near black of the middle por- 

 tion of the tail, the conspicuous white side stripes, and the pure 

 white tip make the tail of spectabilis stand in rather vivid contrast 

 to the pale-brown and whitish tail of deserti. 



The dens of the two larger species of Dipodomys — spectabilis and 

 deserti — can be distinguished at a glance from those of the two 

 smaller — tnerriami and ordii— by the fact that the mounds of the 

 former are usually of considerable size and the burrow mouths are 

 of greater diameter. On the Range Reserve merriami erects no 

 mounds, but excavates its burrows in the open or at the base of 

 Prosopis, Lyciu7n^ or other brush. The mounds of spectabilis are 

 higher than those of deserti, the entrances are larger, and they are 

 located in harder soil (PI. Ill, Fig. 1). The dens of deserti are 

 usually more extensive in surface area than those of spectabilis, and 

 have a greater number of openings (PI. Ill, Fig. 2). 



DESCRIPTION. 



GENERAL CHARACTERS. 



Size large ; ears moderate, ear from crown (taken in dry skin) 9 



or 10 millimeters ; eyes prominent ; whiskers long and sensitive ; fore 



feet short and weak; hind feet long and powerful, provided with 



four well-developed toes; tail very long, usually 30 to 40 per cent 



107600—22 2 



