A Key to the Genera of North American Mammals 



I. AQUATIC MAMMALS WITH THE LIMBS MODIFIED INTO FLIP- 

 PERS FOR SWIMMING. 



A. No external trace of hind limbs; fore pair of flippers fin-like without claws; 



tail broad and flattened horizontally; little or no hair on the body. 

 B. Tail rhomboidal in outline, bluntly pointed at the tip; teeth, i f, c, 



p , m f-4r (Manatee) TRICHECHUS, 26 



BB. Tail broadly forked at the end into two flukes (Whales and Dolphins). 

 C. Mouth enormous, without teeth, but provided with whalebone. 



D. No fin on the back; throat not furrowed BAL^ENA, 13 



DD. Dorsal fin present; throat furrowed longitudinally. 



E. Flippers moderate, edges not scalloped .... BAL^NOPTERA, 16 



EE. Flippers very long, edges scalloped MEGAPTERA, 17 



CC. No visible teeth and no whalebone HYPEROODON, 19 



CCC. Jaws provided with teeth; no whalebone. 



D. A single long tusk, projecting forward, no other teeth. 



MONOCERAS, 24 

 DD. No protruding tusk. 



E. No teeth in the upper jaw. 



F. Teeth in the lower jaw 20-25 on each side. .PHYSETER, 17 

 FF. Teeth in lower jaw 4-14 on each side. 



G. Head protruding beyond the mouth, dorsal fin short, 



tail nearly square behind KOGIA, 18 



GG. Head not protruding, dorsal fin high, tail deeply cleft. 



GRAMPUS, 23 

 FFF. Teeth in lower jaw one on each side. 



G. Teeth at the front of the jaw ZIPHIUS, 19 



GG. Teeth at the middle of the jaw. . . .MESOPLODON, 19 

 EE. Teeth in both jaws. 



F. Teeth few; 8-13 on each side above and below. 



G. Teeth confined to the front portion of the jaws. 



GLOBIOCEPHALUS, 23 

 GG. Teeth distributed all along the jaws. 



H. An enormous dorsal fin, teeth T$-T| ORCA, 33 



HH. Dorsal fin wanting, teeth . . DELPHINAPTERUS, 24 

 FF. Teeth numerous, 22-50 on each side above and below. 

 G. A projecting snout or beak. 



H. Teeth, ff TURSIOPS, 20 



HH. Teeth," fj PRODELPHINUS, 21 



HHH. Teeth, f -ff DELPHINUS, 2 1 



GG. No projecting beak. 



H. Beak a distinct rim; teeth, |f, LAGENORHYNCHUS, 22 



HH. Beak entirely wanting; teeth, ff . . . . PHOC^ENA, 22 



AA. Both fore and. hind flippers well developed, claws or nails present. 



Tail rudimentary; body covered with hair (Seals, etc.). 

 B. Body large and shapeless; long down-pointing tusks in the upper jaw; 



teeth, i |, c {, p f, m $ ODOBENUS, 212 



BB. Shape more graceful; no tusks. 



C. Hind flippers capable of being turned forward for walking when on 



shore. 

 D. A dense soft under fur in addition to the long hairs which cover 



the body; teeth, i f, c 4-, p f , m f- OTOES, 209 



DD. No perceptible soft under fur; molars |. 



E. Back teeth separated from last premolar by a considerable 



space EUMETOPIAS, 211 



EE. Back teeth in a continuous series ZALOPHUS, 211 



CC. Hind flippers permanently directed backward. 



D. A hood-like appendage on the head of the male ; teeth, if, c ^, 



p |, m | CYSTOPHORA, 218 



DD. No hood on the head of the male; teeth i f , c , p f , m |. 



296 



