448 U. Ss. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
veloped into a valve capable of closing the meatus, much more so than in the H. leucopus. 
The thumb is rudimentary, with a broad nail; the posterior portion of the heel is hairy. 
The species of Reithrodon in North America are confined, on the Atlantic border, to the 
southern States ; they are found about St. Louis and westward to the Rocky Mountains, whence 
- specimens were brought by Lieut. Beckwith. Species occur also in New Mexico, Sonora, and 
California. 
I have never seen either skins or skulls of feithrodon from South America; but judging 
from the figures given by Waterhouse, there are considerable differences, not only in size, but 
also in other characteristics. It is, however, impossible to indicate these discrepancies without 
making a careful comparison of specimens from the two continents. 
To Major Leconte is due the credit of first pointing out the existence of Reithrodon as a North 
American genus. 
REITHRODON HUMILIS. 
Harvest Mouse. 
Mus humilis, Avp. & Bacu. Pr. A. N. Sc. Phila. I, Oct. 1841, 97.—Is, J. A. N. Sc. Phila. VII, u, 1842, 300.— 
In. N. Am. Quad. II, 1851, 103; pl. Ixv. 
Hesperomys humilis, Wacner, Wiegm. Archiv, 1843, 11, 51. 
Mus lecontii, Aup. & Bacu. J. A. N. Sc. Phila. VIII, u, 1842, 307.—Is. N. Am. Quad. III, 1854, 324. 
Hesperomys lecontit, WaGNer, Wiegman, Archiv, 1843, 11, 51. 
Reithrodon lecontii, Leconte, Pr. A. N. 8. Phila. VI, Oct. 1853, 413. 
Sp. Cu.—Tail a little shorter than the head and body (about two-tenths of an inch). Head and body less than 2.50 
inches ; usually under 2.25. Hind feet .60. Ears large, with thin membrane covered with short hairs. Color above, 
mouse gray brown, or a little darker ; cheeks, and generally the lower part of the sides, fulvous. Beneath, grayish white, 
tinged with reddish, with a plumbeous aspect. Oral region, chin, and feet, white. 
This animal is considerably smaller than the domestic mouse, (very nearly the size of the 
Mus agrarius of Europe,) but resembles it very much in general appearance; so much so, in 
fact, that the grooved incisors will only distinguish them at first glance. The head is small and 
slender ; the ears are quite large, almost equal to the Hesperomys leucopus.; they are, however, 
apt to appear smaller than in reality, from being partially buried in the fur. They are 
slightly obovate, rounded at the apex, rather longer than wide; the auricle very thin and 
delicate. The antitragus is conspicuously developed as an elongated valve, capable of closing 
the meatus; it is much more distinct than in Hesperomys ; both surfaces are covered with short, 
close hairs, except around the meatus, which is naked. The nose is as in Hesperomys, the 
muffle hairy to the end ; the septum and region round the nostrils naked ; a furrow in the 
middle of the septum continued into a cleft of the upper lip. The eyes are diminutive, smaller 
than in Hesperomys. 
There are no striking peculiarities in the feet; the thumb is rudimentary, armed with a 
broad, short, flat nail. There are six large tubercles on the hind feet and five on the fore, as 
described in Neotoma and Hesperomys. The toes are as in the latter genus. The soles are 
covered with scattered hairs as far as the tubercles, the hairs densest towards the heel. The 
remaining portion is naked, with a pavement of moderately large scales. 
The tail is somewhat variable in length ; usually, however, it is as long as the distance from 
