506 



MONOGRAPHS OF NOUTH AMBRIOAN RODENTIA, 



; 



before me, are probably applicable also to tbose other species of tlie genus 

 of which only dried skins are before me. 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 l)ulbs; one proper to the base of, respect- 

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

 The palm is otherwise uniformly studded with small elevated graimlations, 

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

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

 finger, does not project at all beyond the end of the digit. The whi>' thumb 

 is no more conspicuous than one of the palmar pads. The other dibits 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 etill 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 Crieetodipus, 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 constantly larger than the rest is always observed 

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

 found at Ihe 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 iiears an ordinary claw, 

 tiie 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 thun 

 appears in the case of /'. fasciatus, but the difference is not very striking; it 

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

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

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



