i8o 



MAMMALIA ORDER VII L CE TA CEA. 



Fig. 96.^KiLLER (Oreo, gladiator). 



name from their rapacious habits, and are the only cetaceans which prey on 

 other members of their own order. One killer has been known to swallow 

 Several entire seals one after the other ; and not unfrequently several 



individuals combine forces to 

 attack and kill one of the larger 

 whales, hunting with the per- 

 severance of a pack of hounds. 

 \\ hen swimming near the sur- 

 face of the water, killers may 

 be easily recognised by the great 

 size of the nearly vertical back- 

 fin. The lesser killer ( Pseudorca 

 crassidens), which is also cosmo- 

 politan, and attains a length of 

 about 14 ft., differs from its 

 larger relative by the smaller 

 size of the back-fin, the pointed 

 flippers, and the cylindrical 

 (instead of angulated) roots of 

 the teeth, as well as by the 

 uniformly black colour of the 

 skin. There are generally eight pairs of upper and ten of lower teeth. 



Although the name of black-fish would apply equally well to the foregoing, 

 it is given to the cetacean known scientifically as Globiocephalus melas. 

 The black-fish is characterised by the extremely short and rounded head, the 

 almost uniformly black colour of the skin, and the presence of from eight to 

 twelve pairs of small conical teeth in the front portion of the jaws. The 

 back-fin is long, low, and thick, and the flippers are relatively long and 

 narrow. Generally there is a lance-shaped white patch on the throat. In 

 length, the black-fish, or, as it is often called, pilot-whale, grows to a length 

 of 20 ft. Whether there is more than one species is somewhat uncertain ; 

 but, at anyrate, a form inhabiting the Bay of Bengal is distinguishable by the 

 reduction in the number of the teeth. As regards habits, this cetacean is the 

 most sociable of its order, and since all the members of a herd always blindly 

 follow their leader, enormous numbers are frequently slaughtered at a time. 

 The last of the beakless group of the family is the rare Risso's dolphin 

 (Grampus griseus), which differs from all the other DelphinidcE, save the female 

 of the narwhal, by the absence of upper teeth, while the lower jaw carries 

 only from three to seven small teeth towards its anterior end. In general 

 appearance this species is very similar to the black-fish, although the head is 

 less decidedly globular, and the flippers are rather shorter. It is easily 

 recognised by the peculiar grey striping and mottling of the skin ; scarcely 

 any two individuals being quite alike in this respect. This species is almost 

 cosmopolitan, specimens being stranded from time to time on the British 

 coasts. 



Intermediate, between the beakless and beaked members of the family, ia 

 a genus known as Lagenorhynchus, which includes the various species of 

 short-beaked dolphins. Noticeable on account of their strongly-contrasted 

 black and white coloration, the short-beaked dolphins are characterised as a 

 whole by the short, ill-defined and somewhat ploughshare-like beak of the 

 skull, the moderate size of the back-fin and flippers, and the distinct ridges 

 on the tail. The teeth vary considerably both in size and in number ; but, 



