DOLPHINS 251 



in the Zoological Society's garden. In this individual 

 the doctor noticed the spiny margin to the fin, which 

 has frequently escaped notice in other porpoises, and 

 hence thought that there were two species, one with 

 and one without these spines. It is held by Mr. 

 True that P. brachycium, P. vomerina, and P. lineata 

 (all named by the late Professor Cope) are at most 

 varieties of the common porpoise. 



But Phoccena spinipinnis of Burmeister* is distinct. 

 It has a length of 5 feet 4 inches. Slight beak. 

 Dorsal fin narrow, low, with concave anterior margin. 

 Pectoral fins falcate. End of body ridged above and 

 below. Teeth, 16. 



This porpoise seems to be quite distinct. The 

 specimen upon which the description of Burmeister 

 was based was captured near the mouth of the Rio 

 de la Plata. It is entirely black. But the most 

 remarkable character, which distinguishes it from P. 

 communis, and at the same time allies it to the next 

 species, is the existence of a long, low ridge on both 

 sides of the body near to the tail. This seems to be 

 a survival of the low dorsal ridge of the embryo. 

 (See p. 14.) And the existence of the two ridges 

 gives some colour to older assertions that whales may 

 possess two dorsal fins and an anal fin like the fish. 

 The tubercles on the fin (as well as the peculiar shape 

 of the latter) distinguish the species. They are more 

 numerous and in more rows, on the back as well as 

 on the fin itself. 



* Proc. Zool. Sac., 1865, p. 228. 



