MAMMALS, 
9 
Sp. Ch. —Above, light yellowish brown; lined finely with black; entire sides yellowish rusty, sharply defined against the 
colors of the back and belly. Beneath, pure white; feet and under surface of tail, whitish. Body measuring 2.75 to 3.50 inches; 
tail, 4.50 to 6.00 inches ; hind feet, 1.10 to 1.30 inches. 
One specimen of this species was collected in the Rocky Mountains near the 38th parallel. 
Like all other western specimens, it is considerably larger than more eastern ones. 
REITHRODON MONTANUS, Baird. 
Reithrodon montanus, Baird, Pr. A. N. Sc. Phila. VII, April, 1855, 335 .—Ib. Gen. Rep. Mammals, 1857, 449. 
Sp. Ch. —Tail very little less than head and body, which barely exceed two inches. Hind foot .50. Ears small, the membrane 
thickened, and with long coarse hairs. Above, brown and pale yellowish gray, much lighter than mouse color. Outside of ears 
and flanks, pale yellowish brown, without any rufous. Beneath, dull whitish. 
A specimen was collected in the Rocky mountains, in the parallel of 39°. 
ARVICOLA MODESTA, Baird. 
Arvicola modesta, Baird, Gen. Rep. Mammals, 1857, 535. 
Sp. Ch. —Size of A. pinetorum, or larger. Ears moderate, well furred, rather shorter than the large fore feet, (. 35 to . 40 ) 
Tail vertebrae scarcely longer than the head, (.9;) with the hairs, one-third the head and body. Fur long, soft, . 4 of an inch. 
Above, almost black, hairs with faint yellowish brown tip. Beneath, hoary plumbeous, the line of separation not very 
distinct. Tail like the corresponding regions of the body. Feet dark brown. 
Middle upper molar with five triangles, although the indentations between the two last do not quite meet. 
Two specimens were collected in the Sawatch Pass, (Nos. 16 & 17.) 
