516 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 
As noticed further on, the Cricetedipus parvus of Peale is an uncertain 
animal. In erecting Cricetodipus into a genus, I take C. flavus of Baird as 
the type, and follow this author in distinguishing a second species, which latter 
is probably, but not certainly, the C. parvus of Peale. The two appear to 
constantly differ in the following characters :— 
Tail scarcely or not longer than the head and body; hind foot scarcely or not one-third as long as head 
and body. FLAVUS. 
Tail decidedly longer than head and body ; hind foot more than one-third as long as head and body. : 
ParvuS (of Baird), 
CRICETODIPUS FLAVUS, Baird. 
Yellow Pocket-mouse. 
Perognathus flavus, BatkD, Proc. Acad. Nat. Sci. Phila. 1855, 332.—Batrp, M. N. A. 1857, 423, pl. 8, f. 2, pl. 21 
f.3a-f (assigned to Cricetodipus).—BatrpD, P. R. R. Rep. x, 1859, Gunnison’s and Beck with’s 
Route, Mamm. p. 8.—Batrp, U.S. Mex. B. Surv. ii, pt. ii, 1859, Mamm. 42.—Suckt., P. R. R. 
Rep. xii, pt. ii, 1860, 101 (Montana).—Hayp., Trans, Am. Phil. Soc. xii, 1862, 147 (Loup Fork of 
Platte).—ALLEN, Proce. Bost. Soc. N. H. xxii, 1874, 42 (Yellowstone River). 
Crice‘odipus flavus, GRAY, P. Z. S. 1868, 203 (compiled).—Cougs, Proc. Phila. Acad. 1875, 300 (mono- 
graphic).—Cours & Yarrow, Zool. Exp]. W. 100 Merid. 1875, 109. 
Otognosis flava, COUES, Proc. Phila. Acad. 1875, 305 (provisional name). 
Diacnosis.—Much smaller than Mus musculus; head and body two 
inches; tail the same; hind foot 0.65; ear small, not overtopping the fur, 
simple, without lobe of antitragus or tragus. Soles entirely hairy on the pos- 
terior half. Tail not decidedly longer than the head and body. Hind foot 
scarcely or not one-third as long as head and body. Above, pale buff, inti- 
mately blended with blackish; below, including whole fore leg, snowy white; 
sides with a clear buff stripe; tail obscurely bicolor; white touches often 
found about the ears. 
Haxrrat.—Rocky Mountain region of the United States and eastward in 
the Middle Faunal Province, from the British Possessions (lat. 49°, Cowes) to 
Chihuahua, Mexico. (In the Pacific region replaced by C. parvus.) 
(Description: from numerous alcoholic and dry specimens, including 
Baird’s types )—In general points of exterior conformation, this animal is so 
similar to species of Perognathus already fully treated that the account of 
these features may be abridged. The generic character of structure of the 
ear and hairiness of the sole, with the diminutive size, are the chief points. 
The ear is very small and simple, not overtopping the fur of the parts. It 
is evenly rounded; there is no lobation whatever of either antitragus or 
tragus, the slight notch which exists being formed in front by the folded-over 
edge of the ear itself, and behind by the antitragal ridge. The head is full, 
