PORPOISES AND DOLPHINS 299 



Genus Orcella. 

 THE IRAWADI DOLPHIN {Orcella brevirostris). Fig. 76. 



The Irawadi Dolphin is a small-sized creature of compara- 

 tively restricted distribution. The head is convex from 

 blowhole to upper lip. The line of the mouth, horizontal in 

 front, curves upwards further back to the angle of the gape. 

 The crescentic blowhole is more to the left than to the right 

 side on the top of the head. There is an inconspicuous 

 constriction in the neck region recalling that already described 

 in the White Whale, but the definition of this " neck " depends 

 on the physical condition of the creature, being more obvious 

 when the animal is under-nourished than when it is fat and 

 in good condition. 



The nippers are moderately long and broad triangular 

 structures, the breadth about one-half the length, and the 

 width at the junction with the body about one-half the greatest 

 length. The centre of the dorsal fin is behind the middle of 

 the body. The fin is small and falcate with a rounded point. 

 Behind it on the back and on the under surface posterior to 

 the vent a well-defined ridge extends backward towards the 

 flukes, and ends some 5 inches in front of the notch of 

 the tail. 



The colour of the Irawadi Dolphin is either entirely slate-blue 

 or the ventral surface may be very little paler than the rest. 

 Anderson, in his ' Account of the Zoological Results of two 

 Expeditions to Western Yunnan', from which most of the 

 present description is taken, states that " the young have a 

 distinct moustache occurring about one-half inch above the 

 upper lip and consisting of five brownish bristles . . . the 

 line of the bristles occupying an area of three-quarter 

 inch ". 



The external aperture of the ear in one of Anderson's 

 specimens was 0*08 inches in diameter — a dimension which 

 indicates the almost microscopic size of this opening, as it is 

 found not only in the Irawadi Dolphin, but in members of the 

 family Delphinidae generally. 



Tnere are from 12 to 19 teeth on each side of upper and 

 lower jaws. The number of teeth on one side of the jaw may 



