90 



feed either on the small delicate marine invertebrates which 

 swarm on the living corals, or, if their teeth are adapted for 

 the purpose, on the soft parts of mollusc, which they extract 

 by gnawing or boring holes into the hard substance of the 

 shell. As stated by Haeckel,^ an explanation of the bright 

 colouring of the fishes is found in the Darwinian principle, 

 that the less the predominant colouring of any creature 

 varies from that of its surroundings, the less likely it is to 

 be seen bj' its foes, the more easily it can steal upon its prey, 

 and the more it is fitted for the struggle for existence. 



Conspicuous by their abundance were several species 

 belonging to the family Sclerodermi, including Balistes (file 

 or trigger fish), whose jaws are armed with sharp teeth, and 

 which are said to be injurious to the pearl fishery by preying 

 on the pearl oyster. Present, too, in great numbers, were 

 several species of the family Grymnodontes, Tetrodons 

 (globe or frog fishes), including the beautifully marked 

 little T. margaritatus and Diodons^ which have a bad repu- 

 tation among the natives as being very poisonous. 



ELASMOBEANCHII. 



(Sharks and Rays.) 



FAMILY CAECHAEIID^. 



Carcharias.' — Several young species commonly met with in the 



fish markets. 

 Zygsena malleus. Tuticorin and Pamban. " Hammer-head." 



FAMILY SCYLLIIDiE. 



Stegostoma tigrinum. Tuticorin. 

 Chiloscyllium indicum. Tuticorin. 



FAMILY PEISTID^. 



(Saw-fishes.) 



Pristis cuspidatus. A specimen 1 8 feet in length 



brought on shore at Tuticorin 

 in 1887. 



FAMILY RHINOBATID^. 

 Khinobatus granulatus. Tuticorin. 



' A Visit to Ceylon, Eng. Transl., 1883. 



' The synonymy of Day's Fishes of India and Supplement to the Fishes 

 cf India, 1888, is followed throxighout. 



