PLATAMSTIILE. 589 



coloration D. malayanus being uniform ashy, D. attenuates dark 

 above, ashy grey below, and D. frcenatus dark above, white below, 

 the dark parts spotted or speckled with white. The number of 

 vertebrae is also different. The specimen described by Blyth agreed 

 in colour with D. malayanus ; but if the other forms deserve separa- 

 tion, it is probable that one or both of them will be found on the 

 Indian coasts. D. longirostris, Gray, with teeth |, may also occur*. 

 DelpJiinus velox is not mentioned by True, and must remain a 

 doubtful species for the present. It was founded on a specimen, 

 one of a very numerous shoal, that was harpooned at sea between 

 Ceylon and the Equator. The dorsal and pectoral fins were much 

 falcate, the teeth ^-J ; the colour black throughout. The length of 

 the specimen was 5 feet, the height and base of the dorsal fin 

 each about 5-5 inches, the pectoral 10 inches long, expanse of the 

 tail 13. The movements of these dolphins were very swift, hence 

 the name. The type may have been a young D. malayanus. 



Family PLATANISTIDyE. 



The last family of Cetacea is composed of three genera, each con- 

 taining a single species. All are fluviatile or estuarine ; two are 

 South- American (one, Inia, inhabiting the river Amazons, the 

 other, Pontoporia, living in the Eio de la Plata estuary), and the 

 third, Platanista, is Indian. This distribution may indicate that 

 the family, which in some respects is less specialized than other 

 Cetaceans, was once marine and widely spread, and that the few 

 living representatives, as in the parallel case of Ganoid and Dipnoan 

 fishes, owe their survival to their adaptation for a life in rivers, 

 where the struggle for existence is less severe than in the sea. 



The size of the Platanistidce is relatively small. Teeth are 

 numerous in both jaws, which are long and narrow. The symphysis 

 exceeds half the length of the mandible. The head is divided from 

 the body by a slightly constricted neck. The cervical vertebrae are 

 all free. The tubercular and capitular articulations of the ribs 

 are distinct in front and blend gradually behind as in ordinary 

 mammals. Pterygoids elongate, in contact, not involuted. 



Genus PLATANISTA, Wagler (1830). 



A long compressed beak, slightly enlarged at the extremity; 

 dorsal fin rudimentary, replaced by a low ridge; pectoral fin 



* Owen (Tr. Z. S. vi, p. 23) calls D. longironlris, Gray, the Black Dolphin of 

 the Cape and Ceylon. There is probably some confusion with D. longirostris, 

 Cuv. (V. dussumicri, ante, p. 588), from Malabar. 



