184 Bulletin American Museum of Natural History. [Vol.111, 



sent still another form very different from either. This may be 

 characterized under the name above given, as follows : 



Top of head black, generally varied more or less with gray, through the gray 

 tipping of some of the hairs ; general color above dark gray, the hairs plum- 

 beous at base, subterminally broadly ringed with black and narrowly tipped with 

 white ; a broad nuchal patch, extending generally from the hinder portion of the 

 crown to the shoulders, and more or less on to the sides of the neck, yellowish 

 rufous varied with black, the hairs here being tipped with rusty instead of white ; 

 a very broad area of the same color as the nuchal patch covers the lower back 

 and rump, extending from a point opposite the hips to the base of the tail, and 

 across from one hip to the other. (These patches vary somewhat in size and in 

 the tone of the rufous, which varies from yellowish rusty to brownish rusty. In 

 one specimen these patches are quite pale, and in another nearly obsolete, but 

 in the other ten are conspicuously developed.) Below pure white, in summer 

 pelage (May specimens) the hairs being pure white to the base, in winter speci- 

 mens with the basal portion ashy. The tail, both above and below, is black, 

 washed heavily with white, the hairs of the upper surface being generally wholly 

 black from near the tip to the base, with a long white tip, those of the lower 

 surface white at the extreme base, then narrowly ringed with black, followed by 

 a narrow band of white, and this with a broad band of black and a long white 

 tip. Feet varying from nearly pure white to grayish white ; ears gray varying 

 to blackish, generally more or less tinged with rusty, with a white woolly patch 

 at the posterior inner base, well developed in winter specimens. 



Measurements. Head and body, 250 mm. ; tail, 330 ; total length, 550-600 

 mm. (collector's measurements). Hind foot, 60-63 height of ear from crown, 

 18-20 (from skin). 



Type, No. 1991, Hacienda San Marcos, Tonila, Jalisco, $ ad., May 14, 1889. 



Summer and winter specimens appear to differ only in the pelage in winter being 

 longer and softer than in summer, the fluffy white post-auricular patches better 

 developed, and in the white of the ventral surface being somewhat grayish, from 

 the basal portion of the pelage being ashy. 



While both S. leucops and S. cervicalis have generally distinct 

 rufous nuchal and rump patches, they are very different in the 

 two forms, not only in color but in the position occupied by the 

 rufous portion of the hairs composing these patches. In S. cervi- 

 calis the rusty tint is restricted to the tips of the hairs, and simply 

 replaces the gray tipping of the hairs on the rest of the dorsal 

 surface ; in S. leucops the tips of the hairs of the rump patch are 

 gray, the rufous occupying the subterminal instead of the terminal 

 color zone of the hairs, while in the nuchal patch the rufous 

 occupies all but the extreme base of the hairs. In other words 

 the subterminal color zone in cervicalis is black ; in leucops rufous. 



