1922] MADRAS PEARL FISHERIES 6? 



with young oysters from one month to six months old, those of 

 three to four months of age preponderating. The sizes varied 

 from 10 x \oy 2 x 3% millimetres to 24x22x8% millimetres. The 

 weight of 100 individuals of average size was 99*65 grammes. 



The general facies of the bank approximates closely to that of 

 the Ceylon Periya Par — a bank noted for the frequence of spat 

 falls upon it ; both are of great extent and of diversified character 

 and both lie all but out of sight of land towards the edge of 

 soundings. Great quantities of young oysters were found on the 

 Ceylon bank named in March last, practically of the same age as 

 those on the Tolayiram Par, but on the whole the abundance was 

 distinctly less on the latter bank, while the sand leaves less extent 

 of rock exposed. 



Considerable destruction of the young oysters was apparent, 

 and large numbers of empty shells were found. Of the latter a 

 small proportion, I in 14, bore evidence in the presence of circularly 

 bored holes, to destruction by small carnivorous gastropod molluscs 

 (belonging to the genera Purpura, Nassa and Sistrum) termed Uri 

 by the divers. The great majority, however, furnished no 

 indication to show by what agency death had been caused. Con- 

 sideration of what the chief harmful factor is and how it acts will 

 be dealt with when we deal with the conclusions. 



Characteristic organisms are few in number; sponges pre- 

 dominate, the black crests of Spongtonella nigra being frequent 

 wherever the sand thins away. The pink Petrosia testudinaria is 

 also common, its truncate massive pile increasing the resemblance 

 to a miniature volcano by possessing a crater-shaped excavation 

 upon the summit. Other massive but less conspicuous species are 

 equally abundant, and in some cases, I found the rapid growth of 

 these sponges entailing the destruction of many young oysters, 

 enwrapping and smothering them, as evidenced by the empty 

 shells embedded in the sponge mass. Axinella donnani is occa- 

 sionally met with. 



Corals were scarce. Occasionally locally-isolated colonies, 

 usually small in size, were found, nearly all being Porites, 

 Meandrina, and Astrasids. 



Still less common were Alcyonarians, represented by Sarcophyton 

 Vcrmctus was common on the fragments of calcrete, and the 

 lovely star-fish, Pentaceros lincki, a known enemy of the pearl 

 oyster, was present in considerable numbers. Linckia laevigata 



