506 MONOGRAPHS OF NORTH AMERICAS RODEOTIA. 



before me, are probably applicable also to those other species of the genua 

 of which only dried skins arc before inc. The palm is entirely naked; it 

 presents posteriorly a pair (inner and outer) of immense smooth tubercles, 

 reminding one of the state of the parts in Geomys. Anteriorly, there are three 

 smaller but still very conspicuous bulbs; one proper to the base of, respect- 

 ively, the 2d and 5th digits, and one common to the base of the 3d and 4th. 

 The palm is otherwise uniformly studded with small elevated granulations, 

 and the digits are similarly roughened underneath. The minute thumb ends 

 club-shaped, bearing upon its hack a flat nail, which, like that of the human 

 finger, does not project at all beyond the end of the digit. The whole thumb 

 is no more conspicuous than one of the palmar pads. The other digits bear 

 ordinary claws; the 3d is longest; the 2d and 4th are subequal to each other 

 and but little shorter than the 3d; the 5th is more abbreviated, but its claw- 

 tip still falls beyond the base of the 4th claw. 



As a consequence perhaps of the desert habitat of this species, the 

 nakedness of the soles, which is one of the secondary characters distinguish- 

 ing all the species of Perognathus from those of Cricetodipus, is here carried to 

 an extreme. The sole may be called naked without qualification ; for the 

 fringe of hairs which droops over its sides does not encroach in the least 

 upon the under surface except just at the side of the contracted posterior 

 part of the heel itself. The whole sole is uniformly paved with minute gran- 

 ulations. Among these, one constai.tly larger than the rest is always observed 

 on the inner side about half-way down the metatarsus; and a similar one is 

 found at the base of each of the digits. The digits are marked beneath with 

 transverse lines of impression, and end in smooth, slightly clubbed tips. The 

 first digit, though small, is perfectly formed, and bears an ordinary claw, 

 the tip of which falls opposite the base of the second digit ; the longer 3d 

 digit but slightly exceeds the 2d and 4th. which are about equal to each other; 

 the end of the claw of the 5th digit falls opposite the middle of the 4th one. 



In the development of the hind limbs of this and the next closely allied 

 species of Perognathus, there is more indication of a saltatorial tendency than 

 appears in the ease of P. fasciatus, but the difference is not very striking; it 

 is no more than that which may be inferred on comparison of Cricetodipus 

 parvus with C. flavus, and it falls far short of the state of the case exhibited 

 by Dipodomys. Still, the supposed saltatorial character is further borne out. 



