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U. S. P. R. R. EXP. AND SURVEYS ZOOLOGY GENERAL REPORT. 



I have already referred to some of the differences between this species and H. leucopus. They 

 may always he distinguished by the bright cinnamon color of nuttalli, and especially by the 

 cinnamon ears ; in the other species, though there is an approximation to the bright colors of 

 the back, the ears are always dusky brown, with or without a hoary edging. The under parts, 

 too, of nuttatti are never pure white, but yellowish cinnamon, with the line separating the 

 colors of sides and belly indistinct. 



The skull of this species differs from that of E. leucopus in the broader muzzle, and a greater 

 width of the space between the pterygoid processes. The notch at the posterior portion of the 

 bony palate is thus considerably wider. 



It is with very decided regret that I am impelled, by a strict regard for the law of priority, 

 to change the expressive name of aureolus, hitherto applied exclusively to this species, for the 

 less meaning one of nuttalli. There can, however, be little, if any, doubt that the species 

 described by Harlan, in 1832, belongs to the present animal. It could belong only to one of 

 two species, aureolus of Audubon and Bachman, or leucopus. The description refers to the 

 fawn color of the upper parts, the whitish of the lower, (not sharply defined white as in leucopus,} 

 and concludes by remarking the very striking similarity in color to the Gerbittus canadensis. 

 This comparison would not apply at all to H. leucopus, although very suitable to the other. 

 The figure, moreover, is quite a good representation of the color and size of the species, and 

 indicating very appreciably the cinnamon ears, the indistinct line of demarcation of the colors 

 of back and sides of body and tail, and the extension of the reddish of the sides to the wrist 

 joint. 



The use of Arvicola as the generic term for this animal is quite in accordance with Harlan's 

 views of the genera of North American Kodents, Sigmodon and Neotoma, as well as the Oryzo- 

 mys palustris, being all placed in the same genus. 



List of specimens. 



