176 



MADRAS FISHERIES BULLETIN 



VOL. XIV, 



uncovered at low-tide. They are purely a marine species, never 

 forming beds in backwaters or estuaries, though an occasional 

 individual is sometimes seen among backwater oysters. 



Under favourable conditions they form densely crowded colo- 

 nies upon rocks between tide marks ; the finest example of such 

 beds which I know, is on the rocky shores of St. Mary's Isles, off 

 Malpe, in South Kanara. They are of excellent flavour, but on 

 account of their small size, both natural and often further reduced 

 by overcrowding, as well as the difficulty experienced in opening 

 them by reason of their interlocking edges, they are not of economic 

 importance. 



The third species of South Indian oyster is the COCKSCOMB- 



OYSTER {0. crist again), a massive form 

 occurring singly on stones and shells 

 on the East Coast — Tanjore Coast, 

 Palk Bay and the Gulf of Mannar. 

 The edges of the valves are deeply 

 pleated and these pleats are marked 

 on the surface of the valves as angular 

 ridges and furrows extending radially 

 from the hinge. In the rock oyster 

 similar pleats occur but they are more 

 numerous and much shallower than 

 in the coarsely pleated cockscomb 

 species. 



Several species of PINNA {Pinuidae) 

 occur in Madras waters. The most 

 common one in the Gulf of Mannar is 

 Pinna bicolor, a big wedge-shaped shell 

 often a full foot in length that occurs 

 commonly on sandy bottom on the East 

 Coast. It lives in depths from just 

 below low-tide to about 6 fathoms. 

 The umbones are at the apex of the 

 wedge, the hinge-line along the length 

 of one of the two long sides. It lies 

 buried to half its length or even more, 

 point downwards in the sand, the post- 



FlG. 43. Common Pinna showing 

 byssus. X 5. - 



erior edges gaping. It is quite common 



