A Key to the Genera of North American MammaU 



E. Facial part of head very long; whiskers crenulated. 



Halichcerus, 2i8 

 EE. Facial portion of head short, about equal to the brain-case; 

 whiskers not crenulated. 



F. Muzzle broad, forehead convex Erignathus, 218 



FF. Muzzle narrow, forehead sloping gradually . Phoca, 215-217 



II. AERIAL MAMMALS WITH THE FORE LIMBS MODIFIED FOR 



FLIGHT AND COVERED BY AN ELASTIC MEMBRANE WHICH 

 EXTENDS DOWN THE SIDES OF THE BODY AND BETWEEN 

 THE HIND LEGS (BATS). 



A. Tail wanting; a curious leaf-like appendage on the nose; teeth, if.Cy, 



pi, m I Artibeus, 194 



AA. Tail present; no appendage on the nose. 



B. Tip of tail projecting beyond the interfemoral membrane; teeth, i ^, 



c {, p I, m f Nyctinomus, 195 



BB. Interfemoral membrane reaching to the tip of the tail. 



C. Interfemoral membrane completely covered with fur; teeth, i |, c |, 



p I, m f Lasiurus, 203-205 



CC Interfemoral membrane not completely furred. 



D. Ears very large united by their bases; teeth, i |, c |, p f , m |. 



Corynorhinus, 196 

 DD. Ears not united by their bases. 



E- Upper incisor teeth one on each side close to the canine. 

 F. Size large (length 5.60 ins.) ; teeth, i |^, c }, p i, m |-. 



Dasypterus, 206 

 FF. Size small (length 3.70 ins.); teeth the same. 



Nycticeius, 206 

 EE. Upper incisors two on each side. 



F. Color of fur black with white tips; teeth, i f , c |, p f , m |. 



Lasionycteris, 202 

 FF. Color of fur brown or yellowish brown. 



G. Size large (length 4.60 ins.) ; teeth, i f , c |, p |, m f . 



Vespertilio, 200 

 GG. Size small (length 3.4c ins.). 



H. Teeth, i f, c |, p f, m f Pipistrellus, 201 



HH. Teeth, i f , c f p f , m | Myotis, 196 



III. MAINLY TERRESTRIAL MAMMALS WITH FOUR WELL- 



DEVELOPED LEGS, ADAPTED FOR WALKING.* 



A. Body covered by a bony carapace or shell; teeth, | — | Tatu, 9 



AA. Body covered with hair or fur. 



B. Tail naked and prehensile; ears naked; female with teats opening in 

 a pouch on the belly in which the young are carried; teeth, 



i |, c I, p f , m I Didelphis, 4-8 



BB. Tail not prehensile; ears not naked; no marsupial pouch. 

 C. Toes terminating in hoofs. 



D. Form pig-like; teeth, i f, c |, p |, m f Tayassu, 30 



DD. Form not pig-like; males (and females of same species) with 

 horns. 

 E. Horns hollow, not branched, fitting over a solid bony core; 

 teeth, i f , c J, p |, m f. 



F. Shaggy mane over the head and shoulders Bison, 66 



FF. Long hair over the whole body ; horns massive, Ovibos, 65 

 FFF. Form sheep-like; hair short; horns spiral . . Ovis, 61-65 



*Tbe hind feet are webbed and somewhat flipper-like in the Sea Otter, and in the Plying 

 Squirrel* thtr* it an expansion of skin 00 the sides of the body for flying. 



297 



