264 EXPLORATION OF THE CANONS OF THE COLORADO. 
longest under 0.30. Incisors as usual in the genus. Muzzle almost entirely 
hairy, with a very small naked pad confined between the nostrils. Pouches 
ample, about 1.75 deep (measured from the beginning of the fold of skin at 
the side of the snout). Tail extremely short; under 1.50 in length from the 
true base, and little over 1.00 from the end of the conical enlargement at 
base ; the thinly-haired portion being thus less than one-fourth the total length 
of head and body. Ears minute. Color above pale yellowish-gray, with a 
slight light-brown shade ; the fur plumbeous at base, as usual. Below, nearly 
pure white, the fur being mostly of this color to the very base. No dark 
auricular area. Feet and tail white. Extremity of snout blackish. Claws 
and whiskers colorless. Incisors faced with orange. 
HABITAT. The single specimen of the species at present known, No. 
3051, Museum of the Smithsonian Institution, was taken at Bridgcr's Pass, 
Rocky .Mountains, July 28, 1857, by Dr. W. A. Hammond. 
With only one specimen to go upon, there is little to be added to the 
foregoing diagnosis. That the small size is not due to immaturity is evi 
denced by the fact that the specimen is a female, with functionally-developed 
teats, which had been in use. As well as I can determine from the dried 
skin, there are twelve mammae,* situated as in T. talpoides. In its present 
state, somewhat stretched, the skin measures about 5J inches from nose to 
root of tail. The general dimensions, as well* as the relative and absolute 
length of tail and the proportions of the feet, are all quite beyond the utmost 
limit of variation determined for any other form of Thomomys. It may give 
an idea of the smallness of the feet to say that the hind ones are no larger 
than those of the white-footed mouse (Hesperomys leucopus); they are a 
trifle broader, but not quite so long. The fore feet are decidedly shorter than 
the hinder ones, owing to the slight development of the slender weak claws. 
The ears are minute scarcely larger, comparatively, than in a Geomys, though 
the tiny auricle has the recognizable shape of Thomomys, instead of being a 
mere tumid rim. The tail, as well as can be guessed from the present dried 
state, is less than a fourth as long as the head and body, measured from its 
apparent base. All these characters are utterly incompatible with any variety 
* This appears to be the normal number in this genus ; but, in an alcoholic specimen of talpoides, 
with the fur all gone from the belly, completely exposing the parts, I can find but eight ; the two axillary 
pairs being wanting. 
