1904.] Allen, Mammals from Northwestern Durango. 207 



tinctly intermediate between durangi and aberti, being similar 

 to aberti but with much less white in the tail; two others 

 closely approach ph&urus, having the back gray and the tail 

 as in durangi; the other two are fairly intermediate between 

 durangi and ph&urus. 



An allied and apparently rather unstable form occurs at 

 Colonia Garcia, in northwestern Chihuahua, and may be thus 

 described : 



Sciurus aberti barberi, subsp. nov. 



Type, No. 17503, Am. Mus. Nat. Hist., $ ad., Colonia Garcia, 

 Chihuahua, Oct. 14, 1901; coll. C. M. Barber, for whom the subspecies 

 is named. 



Similar to 5. a. ph&urus, except that the lower surface of the tail is 

 white instead of finely grizzled gray, as in durangi and phaurus. 



Fall pelage. Sides of nose and eyering soiled white ; general color 

 above clear gray, with a subapical pale fulvous suffusion not usually 

 visible except on parting the hairs ; a broad black lateral line ; ventral 

 surface white; upper surface of fore and hind feet white; tail above 

 mixed black and white, very broadly fringed with white, and white 

 below, except at extreme base, as in S. aberti; ears nearly naked, 

 slightly rufous at base outside, with the black ear-tufts about half 

 grown. 



Measurements. Type: Total length, 500 mm. ; tail vertebrae, 240; 

 hind foot, 70. Six adult specimens, all from the type locality, measure: 

 Total length, 507 (500-516); tail vertebras, 237 (220-250); hind foot, 

 71.9 (70-72). 



In the worn summer pelage (May 26-June 18) the gray of the upper 

 parts is duller and more dingy, and the feet are gray instead of white; 

 two specimens out of five show slight traces of red along the middle of 

 the back. 



This form is closely related to true aberti, it considerably 

 exceeding in size either durangi or phceurus, from both of 

 which it differs in having the under surface of the tail heavily 

 washed with white, so that the gray basal portion of the hairs 

 is thinly overlaid by white, while in aberti the hairs of the 

 lower surface of the tail present a solid mass of white, the 

 hairs of the whole lower surface being pure white to the base. 



The above description was originlly based on a series of 

 7 specimens with wholly gray backs, or with only .a slight 



