164 GLIRES. 
I have followed Dr. Coues in the spelling of the specific name of this animal, which 
Gray wrote phillipii; for it was avowedly named in honour of Mr. Phillips, who sent 
home the original type specimen. 
4, PEROGNATHUS. 
Perognathus, Max. zu Wied, Nov. Act. Ac. Cees. Leop.-Car. xix. 1, p. 369 (1839). 
In this genus we have a less specialized type than Dipodomys, characterized by its 
grooved incisors, rooted molars, sparsely haired tail, and more or less naked soles ; 
while the peculiar modification of the skull is not carried nearly so far as in the last 
genus. 
About six species, all natives of the central and western regions of the North- 
American continent, appear to be well established. Of these, two have been separated 
by Professor Baird * and by Dr. Elliott Coues}? under the name of Cricetodipus, the 
former writer treating the group as a subgenus, while the latter raised it to full 
generic rank{. It is true that Perognathus flavus and P. parvus not only differ from 
the other species in the minor external features pointed out by Professor Baird, but 
that Dr. Coues has demonstrated certain cranial characters which show some approach 
to the last genus, and which are, in his opinion, “fully up to the current generic 
mark.” But as these differences are mostly of a comparative nature, and as all the 
species appear to be very closely allied in essentials, I prefer to revert to Professor 
Baird’s views, and to regard Cricetodipus as a subgenus of Perognathus. Following 
this line, the three Mexican Pocket-Mice may be thus diagnosed :— 
A. Cricetodipus (Baird, ex Peale). Ears with no tragal or antitragal lobes. Soles 
hairy on their posterior half. Auditory bulle projecting somewhat behind 
the occipital plane. 
1. P. flavus. Upper parts pale fulvous, mixed with blackish ; lower parts and 
limbs white; a bright fulvous stripe along the flanks. Average length of 
head and body above 2", of tail nearly the same. 
B. Perognathus (proper). Ears with a lobe on the antitragus and usually on the 
tragus. Soles naked to the heel, at least along the centre. Auditory bulla 
hardly projecting behind the occipital plane. 
2. P. hispidus. Upper parts “ yellowish cinnamon, closely lined with blackish ” ; 
lower parts and limbs white; a fulvous stripe along the flanks. Length of 
head and body about 3'"25, of tail rather more. 
* Mamm. N. Am. p. 418 (1857). ft Mon. N.-Am. Rodent. p. 515 (1877). 
t The name Cricetodipus was first applied by Peale to his C. parvus (U.S. Expl. Exp. i. p. 53, 1848, deser. 
orig.), with which Professor Baird identified a Californian specimen now in the United-States National 
Museum. Dr. Coues regards Peale’s species as uncertain, and founds his genus on the “C. jlewus of Baird” 
(Mon. N.-Am. Rodent. p. 516). 
