506 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
before me, are probably applicable also to those other species of the 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 partsin 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 back 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 Perognatnus 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 constartly 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 case 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, 
