184 The Mammals of Colorado 
Conejos County, Colorado, and has also been found on the west 
slope of the same mountains; the record of 5. ahcrti from Florida, 
La Plata County, is, as stated under that species, referable to 
5. mimus. As the type locality of the present form is in north- 
eastern New Mexico, it w^ould seem as if it would be the race in- 
habiting southern Colorado, to the exclusion of true aberti. Its 
northern range is undetermined ; like the next form it is no doubt 
very locally distributed. 
Sciurus aberti ferreus (Lsit ferreus, of or made of iron 
and also used to denote the color of iron, i. e., 
metallic or iron gray). Plain-Backed Squirrel. 
Sciurus aberti concolor True, Proc. U. S. Nat. JMus., xvii., p. 241 
(1894). 
Sciurus aberti ferreus True, Proc. Biol. Soc. Wash., xiii., p. 183 
(1900). 
Type locality. — Loveland, Larimer County, Colorado (William G. 
Smith). 
Measurements. — Total length, 19.3; tail vert., 8.3; hind foot, 
2.3 ; ear, 0.85. 
Description. — Upper parts gray, lacking the chestnut or reddish 
patch ; under surfaces white ; upper side of feet gray, toes white ; 
ears gray with lengthened tufts, black mixed with gray and chest- 
nut; tail alike above and below, gray bordered with black, and 
fringed with white. This race, and very possibly the two preceding, 
though there is no mention of it in the literature at hand, has two 
color phases besides the one just described; in one the animal is a 
uniform dark brown; and in the other it is black all over. In many 
places these two colors are greatly in the majority; on the Divide 
north of Colorado Springs Mr. C. E. Aiken says that only ten per cent, 
of the squirrels are gray, and of the remainder two thirds are black 
and one third brown; this estimate is based on the skins brought 
to him for sale. 
Distribution. — The Plain-backed Squirrel is found along the 
foot-hill districts of eastern Colorado, ranging from 7,000 to 8,000 
feet, chiefly in the yellow pine zone, but it is very irregularly and 
locally distributed. It ranges at least as far north as Fort Collins; 
it is found in some parts, at least, of the Platte Canon region, and 
on the Divide, north of Colorado Springs; I have heard of it near 
Salida, but it is very rare there. 
Habits. — The various forms of Abert's Squirrel are con- 
