A Key to the Genera of North American Mammals 
FFFF. Form goat-like, hair long, pure white . -OREAMNOS, 57 
EE. Horns hollow, forked, and shed periodically; teeth, 1 $,c 8, 
1k eet: ee Ne ee RE yin, as ANTILOCAPRA, 54 
EEE. Horns solid branching antlers, which are shed periodi- 
cally ; teeth, i 2, c $—4, pri, m  . 
F. Nose completely covered with hair .... RANGIFER, 47-54 
FF. Nose not completely haired. 
G. Antlers broadly palmate or flattened....ALcES, 43 
GG. Antlers not flattened. 
H. Animals medium or small; antlers not more than 
twenty-five inches long...... ODOCOILEUS, 34-43 
HH. Animals large; antlers four to five feet. 
CERVUS, 31-34 
CC. Toes terminating in claws. 
D. A gap on each side of the jaws caused by the absence of canine 
teeth. Incisors two in each jaw, large and protruding, 
working against each other like a pair of chisels. 
E. A pair of small rudimentary incisors behind the upper pair 
of large ones. 
F. Tail short; hind legs much longer than the front ones; 
heethy t.Crh, Pay Ml Hees es ciated eee LEPUS, 75-92 
FF. No external tail; legs about equal; p #... .OCHOTONA, 93 
EE. No extra incisors. 
F. Hair interspersed with sharp spine-like quills; teeth, i}, c $, 
DG Tle: Sea cons a yactn's ayia tetegs skeen ens ots ener ee ERETHIZON, 04 
FF. Without spines. 
G. Form mole-like; fore feet modified for digging; no 
external ear; teeth, i+, c $, p 3, m ¢. 
H.. Incisors’ srooved.... ...i2 .54.09S see GEOMYS, 97-99 
HH.» Incisors: not-prooved).....\..2 22s THOMOMYS, 96 
GG. Form not mole-like; fore feet normal. 
H. Body heavy and thick-set, 12-20 inches long exclu- 
sive of tail; legs short. 
I. Tail very, broad, flat, covered with scales; teeth, 
ne ye ome en Ske eae co nner ee er Ate CASTOR, 145-150 
II. Tail long and narrow, flattened vertically, and 
nearly naked teeth, i +, c $3, p $, m 3. 
FIBER, I21-127 
Ill. Tail hairy; teeth,i4,c%, p?—im ?. 
J. Tail very short, less than the “head. 
APLODONTIA, 150 
JJ. Tail moderate, longer than the head, 
ARCTOMYS, 151-159 
HH. Form mouse-like or rat-like; size not larger than a 
common rat (body less than 1o ins. without 
tail); teeth usually,it, c 3, p $, m 3. 
I. Pouches on the sides of the face opening near the 
mouth. 
J. Tail very long; teeth as eae ,PERODIPUS, 100 
JJ. Tail moderate; teeth, 1 ¢, c 3, p 7, m }. 
PEROGNATHUS, 100 
II. No external cheek pouches. 
J. Hind legs much longer than the front ones; 
tail exceeding, head and body; teeth in one 
species,i3,c%, pt+,m ?.. ZAPUS, 102- 105 
JJ... Hind legs not ne dly longer than front ones. 
K. Thick-set, short-legged, short-eared mice of 
the meadow mouse type. 
L. Tail less than one-third the length of 
head and body, generally much less. 
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