424 U. Ss. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
beyond the base of the fourth. The central three toes are nearly equal, the middle one longest; 
the fifth extending a little beyond the last articulation of the fourth toe. A few scattered hairs 
on the under side of the metatarsus. The tail is rather shorter than the body, sparsely coated 
with short hairs. 
The prevailing color of the back and upper part of the sides is a yellowish buff, darkest on 
the back, and with the hairs finely tipped with brownish, clouding the buff; clear pale buff 
along the flanks. On the dorsal region the hairs are plumbeous at their basal half, and buff 
for the remainder, except on the dusky tip. Towards the sides, however, the buff extends 
towards the base of the hairs; reaching this on the line of junction of the belly. The hairs of 
the under parts are snowy white to the roots; the tail paler beneath. Fore leg entirely white. 
This species is smaller than P. monticola ; the tail is shorter and less hairy ; the muzzle is 
shorter. The color above is lighter and less varied, and the lead-colored bases to the hairs less 
extensive, there being none on the sides and beneath. The color is paler than that of P. 
parvus ; the size larger, the tail and feet shorter, &c. 
The acquisition of several specimens in alcohol enables me to give the characters of this 
species, in respect to its external form, with greater precision than as based on the dried speci- 
mens. The head is rather broad and blunt, apparently shorter than in the domestic mouse. 
The eyes are rather minute, situated nearer the ear than the eye. The external ear is low, 
rounded oblong, its longest diameter in a line with the axis of the head. There is no lobe 
whatever on the antitragus, as in P. penicillatus. The ear is sparsely coated with hairs on 
both surfaces, most scattered on the concavity. The muzzle is coated with coarse stiff hairs to 
the very extremity all round ; the septum and region immediately around the nostrils being 
alone naked ; these hairs on the sides and lower part of the muzzle are long, and spring out 
like short fine whiskers. These are long and black, and situated in five rows. The cheek 
pouches are readily capable of eversion, their lining coated with short white hairs. The fore 
claws are rather the longer, the thumb short, though perfectly distinct, and armed with a flat 
nail. The soles are paved from the heel, but are rather thickly studded with short white hairs 
to near the end of the metatarsi. The first toe is very short and set far back, its claw only 
reaching to the base of the second toe ; the central three toes are longest, the middle one exceed- 
ing the others; the fifth toe is situated posterior to these, and its claw reaches the penultimate 
articulation of the fourth. The tail is formed as in the mice, cylindrical, tapering to a rather 
blunt tip; it is covered with whorls of fine scales, with short hairs springing between them, 
but not obscuring the whorls ; there is a short pencil of stiff hairs at the end. ‘The tail, with 
the hairs, is about equal to the head and body in length, or barely less. 
A specimen (2615) from the Upper Missouri is rather larger, and the prevailing colors above 
appear more slaty ; the lower part of the sides yellow, or rather yellowish orange. This, how- 
ever, is probably of not much importance, as there is a similar difference in specimens caught 
on the Mexican boundary line. 
