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, c?, 
ped; mi t$—t+ (Manatee)... cae. ce eee hee TRICHECHUS, 26 
BB. Tail broadly forked at the end into two flukes (Whales and Dolphins). 
C. Mouth enormous, without teeth, but provided with whalebone. 
D. No fin on the back; throat not furrowed........ BALANA, 13 
DD. Dorsal fin present; throat furrowed longitudinally. 
E. Flippers moderate, edges not scalloped....BAL@NOPTERA, 16 
EE. Flippers very long, edges scalloped......MEGAPTERA, 17 
CC. No visible teeth and no whalebone.......... HYPEROODON, 19 
CCC. Jaws provided with teeth; no whalebone. 
D. A single long tusk, projecting forward, no other teeth. 
MONOCERAS, 24 
DD. No protruding tusk. 
E. No teeth in the upper jaw. 
F. Teeth in the lower jaw 20-25 on each side..PHYSETER, 17 
FF. Teeth in lower jaw 4-14 on each side. 
G. Head protruding beyond the mouth, dorsal fin short, 
tail nearly square ;behind:. <7. .c 727 sini Koeia, 18 
GG. Head not protruding, dorsal fin high, tail deeply cleft. 
GRAMPUS, 23 
FFF. Teeth in lower jaw one on each side. 
G. Teeth at the front of the jaw............ ZIPHIUS, 19 
GG. Teeth at the middle of the jaw....MESOPLODON, 19 
EE. Teeth in both jaws. 
F. Teeth few; 8-13 on each side above and below. 
G. Teeth confined to the front portion of the jaws. 
GLOBIOCEPHALUS, 23 
GG. Teeth distributed all along the jaws. 
An enormous dorsal fin, teeth 4$-48...... 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. 
A. A -Weehh 085 2. . career ehehy och onsen Seas Sete one TURSIOPS, 20 
AU... SWeeth; 325 ci. Henan ays wr ales PRODELPHINUS, 21 
HHH... Teeth, $732 3 ioc. keene: DELPHINUS, 21 
GG. No projecting beak. 
H. Beakadistinct rim; teeth, 35, LAGENORHYNCHUS, 22 
HH.  Beakentirely wanting; teeth, #8....PHOCHNA, 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; 4.4, c.4, D240. Fe ae ee ee eee 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; 1 £, ¢4+,p4, 1m #s..0 05602... 10% Oroxrs, 209 
DD. No perceptible soft under fur; molars }. 
E. Back teeth separated from last premolar by a considerable 
BNACE TAN te. aba ants oe scien oom cee EuUMETOPIAS, 211 
EE. Back teeth in a continuous series........ ZALOPHUS, 2II 
CC. Hind flippers permanently directed backward. 
D. A hood-like appendage on the head of the male; teeth, i ¢, e +, 
i SY, Bee so lahale etre tam ee aie wich vee aire CYSTOPHORA, 218 
DD. No ood on the head of the male; teeth i }, c }, p $, m . 
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