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216 



MONOQIIAPHS OP NORTH AMERICAN RODBNTIA. 



was leil of it but some coimninutud fragments of the tikull, some loose teeth, 

 bones of the font, and a few whiskers. Most fortunately, however, the back 

 upper molar was not lost, and this furnished perfect identification. Accord- 

 ing to Cope's measurements, his animal was smaller than any others we have 

 seen, iiut not much !<o ; nor is there, in other respects, any discrepancy 

 sufficient to cast suspicion on the identification we make. 



No. 4172. — Very light gray, with a noticeable darker (brownish-black) 

 dorsal area, so much restricted as to appear alaiosl like a dorsal stripe. 

 Belo'.v, nearly white, but little soiled, and the pale plumbeous bases of the 

 hairs little apparent ; tail short, light brown above, white below ; feet above 

 nearly white. (Dimensions as below.) 



No. 10268 (Great Plains, Washington Territory ; type of pauperrima 

 Cooper). — Identical with the last, but the dorsal darkness pretty uniformly 

 distributed. (Dimensions as below.) Tail very short. 



No. 3056. — One of the palest Arvicolas we ever saw except ''breweri". 

 Above, uniform dull pale gray, with scarcely a brown shade and no blackish; 

 below, hoary white, almost as pure as in a Hesperomys on the ends of the 

 hairs, but these are so short (the animal was killed in August, probably a 

 young of the year) that their plumbeous bases give the predominant shade; 

 tail and feet hoary whitish; tail extremely short. (Dimensions as below.) 

 The pallor of this specimen is parallel with that of all the other Muridee of 

 the same region. 



No. 324-1. — Upper parts an intimate grizzle of gray and brown in equal 

 parts, little if any blackish; below of ordinary riparius color; feet and tail 

 brown above; tail short, but its caliber as well as its length undue, because 

 a stout peg has been thrust into its skin after removal of the vertebrae. 

 Rather exceeding any of the foregoing in size (see below). Approximating 

 in color to the next, viz : — 



No. 3055. — Rather larger than any of the foregoing, even allowing much 

 for the evident overstuffing; but tail short. In color, almost exactly like the 

 paler "-haydeni'' stripe of auslerus; the hoary groy of the belly quite muddy. 



With only the type of curtatu* before us, together with the Californian, 

 Washington, and Utah speeime|is, we could not have hesitated in admitting 

 the species. But the precisely intermediate Kansas and Nebraska speci- 

 mens prove that a truer rendering of the facts in the case will be to hold 

 curtatus for a geographical differentiation of austcrus. It will be recollected 



