516 MONOGRAPHS OF NORTH AMERICAN RODENTIA. 



As noticed further on, the C/icetodipus parvus of Peale is an uncertain 

 animal. In erecting Cricetodipus into a genus, I take C. Jlavus of Baird as 

 the type, and follow this author in distinguishing a second species, which latter 

 is probably, l»ut nol certainly, the C. parvus of Peale. The two appear to 

 constantly differ in the following characters: — 



Tail scarcely or not longer than thu head and body ; liind foot scarcely or not one-third as long as head 

 and body. fi.avus. 



Tail decidedly longer than head and body ; hind loot more than one-third as long as head and body. 



parvus (of Baird). 



CRICETODIPUS FLAVUS, Baird. 



Yellow Pocket-mouse. 



P< rognathus flanis, Bairh, Proc. Acad. Nat. Sci. Phila. 1855, 332.— Baird, M. N. A. 1857, 423, pi. 8, f. 2, pi. 21 

 f. 3a-/ (assigned to Cricetodipus). — Baird, P. R. R. Rep. x, 1659, Gunnison's and Beekwith's 

 Route, Maraiu. p. 8.— Baird, U. S. Mex. B. Surv. ii, pt. ii, 1859, Mamm. 42.— Suckl., P. R. R. 

 Rep. xii, pt. ii, I860, 101 (Montana). — Hayd., Trans. Am. Phil. Soc. xii, 1862, 147 (Loup Pork of 

 Platte).— ALLEN, Proc. Bost. Soc. N. H. xxii, 1874, 42 (Yellowstone River). ' 



Crice'odipus flavns, Gray, P. Z. S. 1868, 203 (compiled.).— Coues, Proc. Phila. Acad. 1875, 300 (urouo- 

 graphio).— Coues & Yarrow, Zobl. Expl. W. 100 Merid. 1875, 109. 



Otognosis flava, Coues, Proc. Phila. Acad. 1875, 305 (provisional name). 



Diagnosis. — Much smaller than Mas 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. 



Habitat. — Rocky Mountain region of the United States and eastward in 

 the Middle Faunal Province, from the British Possessions (hit. 49°, Coues) to 

 Chihuahua, Mexico. (In the Pacific region replaced by C. j?arvus.) 



(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 Perognatltus 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 lull, 



