PORPOISES .AND DOLPHINS 307 



With these complications in mind it may be said, however, 

 that " porpoise " refers to those members of the family 

 Delphinidte that are small in size, are beakless, have a triangular 

 dorsal fin and spade-shaped teeth ; and that " dolphin " 

 embraces the remaining members of the family except the 

 larger forms, as for instance the Killer, dignified by the name 

 of " whale ". 



Genus Phoccena. 



THE COMMON PORPOISE (Phoccena phocama) PI. VIII a. 



Fig. 94. 



The Common Porpoise is by far the most abundantly- 

 occurring Cetacean in British seas ; to such an extent does it 

 predominate that even when rarer visitors make an appearance 

 the tendency is to say that they are also porpoises if they 

 approximate at all to the size of this species. Yet the Common 

 Porpoise is very easy to distinguish, even in the water, by its 

 small size, beakless head and triangular back fin. It is a 

 rather stoutly built little animal, having its greatest diameter 

 in the region midway between insertion of flippers and dorsal 

 fin. Behind the dorsal fin the body tapers off to the junction 

 of tail stock with flukes, without either dorsal or ventral 

 ridges such as are found in some related species. The dorsal 

 fin is situated slightly behind the middle of the body, and is 

 low and only very slightly, if at all, concave on its posterior 

 border. The flippers are almost oval in outline, rather blunt 

 at the tip and small in proportion to the size of the animal. 



Sometimes the front margins of flippers and dorsal fin have 

 on them a number of little prominences or blunt spines. The 

 species P. titbercidifera was created to receive animals so 

 adorned, but now it is not usual to regard them as distinct 

 from the Common Porpoise. 



The Common Porpoise is black on the back and white on 

 the belly ; the flippers, flukes and the stock of the tail are 

 also black. Between the pigmentation of the back and the 

 white of the belly is on the sides a grey or whitish area which 

 varies in size and in shade. The junction of the flipper with 

 the body is usually in the white region, and from the flipper 



