PORPOISES AND DOLPHINS 311 



DALL'S HARBOUR PORPOISE (Phoccena dallii). 



This Porpoise differs from the Common Porpoise in coloration, 

 the shape of the back fin and tail stock. The body is black 

 except for an area of white on under surface and sides in the 

 hinder half of the body. The dorsal fin is white at the tip, 

 and has a slight concavity on the hinder margin just below it. 

 The front margin bears faintly marked tubercles. The tail 

 stock is furnished with a dorsal and ventral ridge, as in 

 Burmeister's Porpoise. The lower jaw projects slightly 

 beyond the upper. The teeth are very small ; there are 23 

 on each side of the upper jaw and 27 on each side of the lower. 

 The total length is less than 5 feet. It is known from the coast 

 of Alaska and is very rare. 



TRUE'S PORPOISE {Phoccena [Phoccenoides] truei). 



Fig. 79. 



This species and the preceding one have been placed by 

 Dr. R. C. Andrews in a genus by themselves — Phoccenoides— on 

 account of distinctive colour, extremely small teeth and greatly 

 increased number of vertebrae in the backbone — there are 

 about 30 more than in the Common Porpoise and Burmeister's 

 Porpoise which have just over 60. P. truei is like Dall's 

 Porpoise, but is distinguished from it by having the white 

 area on the sides extending forward beyond the insertion of 

 the flippers. The back between dorsal fin and tail is raised into 

 a ridge so that the outline of this region of the body is almost 

 horizontal until near the flukes, where it dips down abruptly 

 to the junction of these with the tail stock. There is a distinc- 

 tive trident-shaped extension of the black into the whiteness 

 of the ventral surface in the region of the vent. As in Dall's 

 Porpoise, the lower lip projects slightly beyond the upper. 

 The teeth are exceedingly small, 19 on each side of the upper 

 jaw and 22 on each side of the lower. The length of P. truei is 

 just under 5 feet, and it is only known from the coast of 

 Japan. 



