16 MADRAS FISHERIES BULLETIN VOL. XI, 



corresponding series of furrows in the lower valve. Externally 

 the shell is tinted an opaque pinkish purple. Internally it is white, 

 margined with purple or black. The size is generally smaller than 

 that of the ordinary backwater or mud-oyster and seldom exceeds 

 three inches in length. 



The habitat of rock oysters is a narrow band between tide 

 marks ; during ordinary spring tides, these oysters are entirely 

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

 forming beds in backwaters or estuaries, though an occasional 

 dwarfed individual is occasionally to be seen among backwater 

 oysters. 



Under favourable conditions they form densely crowded colonies 

 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 over- 

 crowding, as well as the difficulty experienced in opening them by 

 reason of their interlocking edges, they are not of any economic 

 importance. 



BACKWATER CLAMS. 



At least four estuarine clams of value as food are found in the 

 Presidency, namely : — 



Mcrctrix nicretrix, M. casta, M. casta var. ovum, and Vclorita 

 cochinensis. (See Fig. 4). 



The first of these is comparatively scarce, and the third, which 

 is of chief importance in Malabar, is not found on the east coast 

 where M. casta takes its place as the most abundant of backwater 

 clams. 



THE Small Clams (Meretrix casta and M. casta var. 



OVUM). 

 Tamil^ — Matti (ujtlia.). 



Malayalam — Eninthti at Calicut ; Kakka at Cochin. 



Everywhere along the coast from South Kanara in the west 

 round to Ganjam in the east, with the exception of the Gulf of 

 Mannar and Palk Bay, either one or other of these little clams is 

 found abundantly in muddy sand in estuaries and connected back- 

 waters wherever the water remains saline throughout the greater 

 part of the year. Suitable conditions prevail over more extensive 

 areas on the west coast, and it is there, par excellence, that these 

 clams attain their greatest importance. 



