SACCOMYID A—PEROGNATHIDINA—P. PENICILLATUOS. 505 
Hasrrat.—The Basin of the Colorado River. (The very few specimens 
at present known to naturalists have all come from Arizona and the adjoining 
border of Southern California.) 
(Description from Woodhouse’s type, which is mounted, and several 
more recent specimens, dry and alcoholic.) In all the other species of Pero- 
gnathus given on these pages, the tail, whether longer than the body or decid- 
edly shorter, is simply haired, with the terminal hairs no longer than those 
surrounding the tail. The present species is therefore remarkably distin- 
guished by the comb or crest of long hairs on the terminal third or more of 
the member, produced by a gradual lengthening until those at the end are 
half an inch or more in length, producing a penicillate brush proportionally 
as long as that of some species of Tamias or even Sciurus. With this singu- 
lar character others of equal tangibility are cobrdinated. The description to 
be given will include some points common to the genus, as, with one excep- 
tion, the present is the only species of Perognathus of which I have speci- 
mens in the flesh. 
The head is about one-third of the total length of head and body; broad 
and full across the temporal and orbital regions, thence tapering rapidly to 
the produced but rather blunt snout. The muzzle is entirely and densely 
pilous excepting a small nasal pad, with a median furrow; the nostrils are 
very small and irregular in contour. The long upper lip is heavily clothed 
with stiffish hairs, forming a fringe which droops over and hides the incisors. 
The whiskers are numerous and very fine; besides the labial set, the longest 
of which much exceed the head in length, there are others about the eye and 
ear. The eye is of moderate size, and situated much nearer to the ear than 
to the nose. The ear shows very conspicuously the prominent lobe of the 
antitragus, which is the chief external peculiarity of this genus, as compared 
with Cricetodipus ; and opposite to if, on the other side of the notch, there is 
a similar and smaller, but still very evident, tubercle just within the border 
of the ear. These two prominences together cause the notch of the ear to 
be very strongly defined; and the margin of the external ear is altogether 
excluded from the notch. The contour of the ear is broadly rounded. ‘The 
slit of the cheek-pouch is about half an inch long, beginning on the side of 
the upper lip and curving around with a free border to near the angle of the 
Jaw, there being but narrowly separated from its fellow. 
The details of the palms and soles, as clearly made out from the material 
