A Key to the Genera of North American Mammais 



FFFF. Form goat-like, hair long, pure white . .Oreamnos, 57 

 EE. Horns hollow, forked, and shed periodically; teeth, i |, c g, 



p f, m f Antilocapra, 54 



EEE. Horns solid branching antlers, which are shed periodi- 

 cally ; teeth, i J, c § — J, p |, m f . 

 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 protrtiding. 



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; 



teeth, i f , c §, p f, m I 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 g, 



p g, m| Erethizon, 94 



FF. Without spines. 



G. Form mole-hke; fore feet modified for digging; no 

 external ear; teeth, i j, c §, p g, m |. 



H. Incisors grooved Geomys, 97-99 



HH. Incisors not grooved 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, 



i I, c §, p 1, m I Castor, 145-15° 



II. Tail long and narrow, flattened vertically, and 



nearly naked teeth, i |, c §, p §, m |. 



Fiber, 121-127 



III. Tail hairy; teeth, i |, c §, p |— { m |. 



J. Tail very short, less than the head. 



Aplodontia, 150 

 J I . 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 10 ins. without 

 tail); teeth usually, i|, c g-, p g, m f. 



I. Pouches on the sides of the face opening near the 



mouth. 

 J. Tail very long; teeth as above. Perodipus, 100 

 JJ. Tail moderate; teeth, i j, c 1 p j, m f. 



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, i \, c g, p }, m J . . . .Zapus, 102-105 



JJ. Hmd legs not markedlv 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. 



»9« 



