io8 The Mammals of Colorado 
sometimes almost as bushy as that of a squirrel, and some- 
times round and scantily haired, more like that of a true 
rat; skull long and narrow, with a long rostrum; nasals ex- 
tending back behind the premaxillae; palate ending about 
opposite the end of the last molar; molars rooted, but with 
folded enamel plates simulating the appearance of those of 
the MicrotincB; swelling of the root of the lower incisors on 
the outside of the mandible. 
A small subfamily confined to North America. 
Genus NEOTOMA (Grk. ncos, new -f- temncin, to cut). 
Neotoma Say & Ord., Joiir. Acad. Nat. Set. Phila., iv., p. 345 
(1825). Type N. floridana. 
Revision, Merriam, Proc. Acad. Nat. Sci. Phila., p. 244 (1894). 
Fore feet with the first digit with a rudimentary nail ; hind feet 
with five digits, all clawed; sole with the usual pads and fairly 
thickly clothed with hair; skull with the cranium not abruptly 
constricted in front of the brain-case ; anteorbital foramen wide 
above, compressed into a somewhat narrow slit below; dentition, 
i. ^;m. I X 2 = 16; incisors broad and smooth; molars prismatic, 
rooted or semi-rooted; crowns flat, their sides invested with enamel 
forming a series of salient loops and reentrant angles; crown of 
posterior lower molar never S-shaped, but with a single loop ex- 
ternally and internally. 
Some fifty species of these large rats have been described, 
chiefly from the southern parts of the United States and 
from Mexico, though one or two species extend northward 
into British Columbia, Alberta, and Yukon, and perhaps 
Alaska. Eight of these have been met with in Colorado 
and can be distinguished as follows : 
Key of the Species 
A. Tail round, short-haired, smooth, and tapering; hind feet 
comparatively short. (Subgenus Neotoma.) 
a. Gray above, without rufous tinge; pure white below. 
a'. Larger, total length 13.5 or more; tail short, hardly f 
length of head and body. N. micropus, p. 109 
b'. Smaller, total length about 13.0; tail long, more than 
f length of head and body. N. albigula warreni, p. 1 1 1 
