270 A BOOK OP WHALES 



there are a number of forms existing in the rivers 



<_> 



of South America to which, at any rate, five names 

 have been given. But what differences separate 

 S. guianensis of van Beneden, 5". brasiliensis of the 

 same, S. p alii da of Gervais, .5*. tucuxi of Gray, from 

 each other and from S. fluviatilis of Gervais is a 

 matter which is not ripe for decision, barely, indeed, 

 for discussion. Mr. True thinks that the two marine 

 forms ,5. guianensis and .S. brasiliensis are distinct 

 from the remaining, which are fluviatile. We shall 

 accept what seems to be in itself a reasonable view. 



Sotalia guianensis, of van Beneden ( = Sot 'alia 

 brasiliensis, Id.),* is in, colour black or brown, white 

 below. Teeth, 29-34. Vertebrae, 54 (55), of which 

 ii or 12 dorsal. 



The example of Sotalia brasiliensis studied by 

 van Beneden was a smaller individual than that of 

 S. guianensis, itself a fact tending to throw doubt 

 upon the distinctness of the two forms, considering 

 the minute points of difference which distinguish 

 them. However, Professor van Beneden's coloured 

 figure of S. brasiliensis shows an animal which is 

 largely of a pale brown colour. But this is by no 

 means without the boundaries of colour variation, 

 so little known, as must be constantly insisted upon 

 among the whales. Goeldi, who has lately re- 

 investigated the species " brasiliensis, y 'f thinks that 



* Mem. Ac. Roy. Belg., xli., 1875. 



t Zool.Jahrb. Syst. Abth., iii., iSSS, p. 134. 



