3l8 WHALES AND DOLPHINS 



COMMERSON'S DOLPHIN (Cephalorhynchus commersonii) . 

 PI. VIII b. Fig. 85. 



Commerson's Dolphin is perhaps the most conspicuously 

 marked small cetacean to be found in the Southern Ocean. 

 It has the alternative common names of Piebald Porpoise and 

 Le Jacobite, the latter Commerson's own name for it ; both 

 names refer to the striking black and white colour of the body. 



The head is conical in form with very ill-defined or indistin- 

 guishable beak. The dorsal fin, situated slightly behind the 

 middle of the back, is broadly rounded at the tip and reclined 

 backward. The flippers are rounded, not tapering at the tip, 

 and the general outline is elliptical. The posterior margin of 

 the flukes is not so pronouncedly concave as in some of the 

 foregoing species. The distribution of pigmentation, which is 

 a deep black, sharply separated from the pure whiteness of 

 the unpigmented portion, makes this species unmistakable. 

 The whole of the head is black, but enclosed within the 

 pigmented under surface is a pear-shaped area of white in 

 the region of the chin and throat. The flippers are inserted in 

 the backward extension of the blackness of the head and are 

 themselves pigmented. A promontory of black on the under 

 surface projects back towards the middle of the belly. The 

 greater part of the belly is white, but surrounding the repro- 

 ductive aperture is a patch of pigment. On the back pigment 

 extends obliquely from in front of the back fin to the tail 

 flukes. There are 29 or 30 pairs of teeth in upper and lower 

 jaws. 



The body length is up to 5 \ feet. 



The range of distribution of this species is in the region at 

 the southern end of South America. It has been observed in 

 the Straits of Magellan, near Tierra del Fuego and at the 

 Falkland Islands. 



Sir Sidney Harmer suggests in a paper dealing with this 

 species that the striking markings on the body may have 

 protective value to the animal : "As seen in the water, the 

 white area probably divides the body into two parts, which 

 seem to have little if any connection with one another. The 

 dolphin is in fact effectively camouflaged, and perhaps the 

 protection is specially successful in water liable to contain 



