300 PROCEEDINGS OF THE ACADEMY OF 



II. Genus CRICETODIPUS (Baird). 

 ? Cricetodipus, Peale, U. S. Expl. Exped. 1848, 52. Type - 



= Cricetodipus, Baird, M. N. A. 1858, 418. Type Perognathus flavus. Gray, P. Z. S. 

 1868, 202. 



In treating of this form as a subgenus of Perognathus, Prof. 

 Baird clearly showed its external peculiarities, namely, absence 

 of Jobation of the antitragus, hairy soles, and diminutive size; to 

 these points are to be added the cranial peculiarities coincident 

 with decidedly greater development of the mastoid than that seen 

 in Perognathus. The points having already been given, it is need- 

 less to recapitulate them. 



As noticed further on, the Cricetodipus parvus of Peale is an 

 uncertain animal. In erecting Cricetodipus into a genus, I take 

 P. flavus of Baird as the type, and follow this author in distin- 

 guishing a second species, which latter is probably, but not cer- 

 tainty, the P. 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. 



Perognathus flavus, Baird, Proc. Acad. Nat. Sci. Phila. 1855,' 332. Baird, 



M. N. A. 1857, 423, pi. 8, f. 2, pi. 21, f. 3 a-f( assigned to Cricetodipus). 



Baird, P. R. R. Rep. x. 1859, Gunnison's and Beckwith's Route, 



Mamm. p. 8. Baird, U. S. Mex. B. Surv. ii. pt. ii. 1859, Mamm. 



p. Suckl., P. R. R. Rep. xii. pt. ii. 1860, 101 (Montana). 



Hayd., Trans. Am. Phil. Soc. xii. 1862, 147 (Loup Fork of Platte;. 



Allen, Proc. Bost. Soc. N. H. xxii. 1874, 42 (Yellowstone R.). 

 Cricetodipus flavus, Gray, P. Z. S. 1868, 203 (compiled). 



Diagn. 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 en- 

 tirely hairy on the posterior 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, intimately blended with black- 

 ish ; below, including whole fore leg, snowy white ; sides with a 

 clear buff stripe; tail obscurely bicolor ; white touches often found 

 about the ears. 



Hab. Rocky Mountains of the United States and eastward in 



