56 Miller Description of a New White-Footed Mouse 



young always passing through a gray phase before assuming the 

 fulvous pelage ; tail always sharply bicolor. 



Adult (9 No. \Hl, collection of G. S. Miller, Jr., Peterboro, 

 Madison county, N. Y., July 24, 1892) ; length, 200* ; tail verte- 

 bra 1 . 100; pencil, 6.6; hind foot, 21.4 ; ear from notch, 19; ratio 

 of tail vertebra) to total length, 50. Fur everywhere except on 

 lips and chin, slaty plumbeous at base. Dorsal surface wood- 

 brown, slightly tinged with yellow, and very sparsely sprinkled 

 with blackish hairs, which form a faint, ill-defined dorsal stripe; 

 area between ears somewhat grayer ; ears thinly clothed with 

 whitish hairs internally, externally with brown ; a whitish tuft 

 at anterior base of ear ; whiskers reaching about to shoulders, 

 mixed blackish and silvery : tail sharply bicolor, white ventrally 

 and at extreme tip, Vandyke brown above; dorsum of man us 

 and pes, together with whole ventral surface, soiled white. 



Young in gray phase (9 No. }J|, collection of G. S. Miller, 

 Jr., Peterboro, Madison county, N. Y., August 1, 1892) ; length, 

 201; tail vertebra?, 105 ; pencil, 11; hind foot, 21; ear from 

 notch. 17.8 ; ratio of tail vertebrae to total length, 52.2 ; con- 

 tained three embryos. Color of dorsal surface intermediate be- 

 tween broccoli-brown and smoke gray, with a slight admixture 

 of blackish hairs as in adult, and a very faint trace of a narrow 

 yellowish line bordering white of belly ; a clear smoke-gray area 

 between ears ; otherwise colored like adult, except that the dorsal 

 stripe on the tail is somewhat darker. 



On comparing over one hundred specimens of Sitomys ameri- 

 canus canadensis with about four hundred skins of S. amencanus 

 the longer, more hairy tails and, as a whole, grayer color of the 

 former are very noticeable. Three " stages of development " may 

 conveniently be recognized in these mammals : first, the plumbe- 

 ous young ; second, fully grown and sexually mature individuals 

 with the teeth still unworn, and, third, old animals with worn 

 teeth. In the first stage there is nothing to distinguish the two 

 subspecies except the longer, more hairy tail of S. canad&wis. 

 Specimens in the second stage differ most markedly, as S. cana- 

 densis is now gray, while S. americanus has, for the most part, 

 assumed the russet coat. In the third stage again the two forms 

 resemble each other somewhat closely, since both are now in 

 the fulvous pelage; canadensis, however, may always be distin- 

 guished from its smaller relative by its longer, more hairy, and 



* All measurements are in millimeters, unless otherwise specified. 



