302 PROCEEDINGS OP THE ACADEMY OF 



In most cases, any difference which may be observed is the other 

 way, the tail being if anything a little shorter than the head and 

 body. The tail, as in other species of this genus and of Perognathus 

 (except P. penicillatus) is closel}', but not very thicklv, haired 

 uniformly throughout ; the terminal pencil is about a tenth of 

 an inch long. 



The pelage is extremely fine, soft, and gloss}\ The pictura is 

 the same as in other species of this genus and Perognathus, 

 namely, colored above with blended light and dark tints, white 

 below, with a clear, single-color stripe along the sides. The 

 upper parts are an intimate mixture of pale yellowish-buff with 

 dark brown or blackish ; the hairs are clear lead-color basally, 

 then buff-ringed, then most of them dark-tipped. The resulting 

 tone is nearly uniform over all the upper parts ; but there are 

 liable to appear whitish ortawn}^ touches about the ears and eyes, 

 and an appearance of a dark streak along the side of the head. 

 The fawn-colored lateral stripe is uninterrupted from nose to heels ; 

 the tint is rather brighter than the buff of the upper parts, and 

 pure, being not mixed with any dusky, and the color extending to 

 the roots of the hairs. The entire under parts, including the whole 

 fore leg, the hind feet, and inner side of hind leg are snowy white, 

 the hairs having no basal color. The tail is obscurely bicolor ; 

 white below, and not very sharply colored above to correspond 

 with the areas of the body. 



Veiy young specimens, though nearly full grown and showing 

 a sharp lateral streak, are more simply colored above than the 

 adults, being grayish with extremely faint bufty lining, instead of 

 sharply blackish and buff. There is also observable, in the series 

 before me, a tendency to exhibit two different tones of coloration. 

 Those from dry regions east of the mountains are mixed gra3 7 ish- 

 brown and grayish-buff, with the lateral pale buff stripe not very 

 conspicuous. In New Mexico, southern Texas, and southward 

 the animal frequently assumes a ruddier shade of the light color, 

 mixed with much less blackish ; in these, the lateral stripe is quite 

 indistinct, because the upper parts in general are not very different. 

 But the distinctions in these cases are not strong enough to require 

 anything further than this notice of the fact. 



The following table of measurements will illustrate the size and 

 shape of the species very fairly, and to some extent expose the 

 ran are of variation. 



