Under the microscope this coating is seen to consist of a basal 

 layer of short green conferva rooted to the surface of the shell, 

 while the tangled filaments are smothered and hidden by a dense 

 gathering of myriads of diatoms of many genera and species, 

 many sponge spicules, minute grains of sand, and a large bulk 

 of mud particles ; a delicate red brown filamentous alga is also 

 frequently present as a principal constituent of the feltlike 

 covering. 



The higher clusters of oysters, those exposed each tide, are 

 otherwise almost bare of adhering organisms ; those in deeper 

 water which are never uncovered are usually veiled by a 

 luxuriant growth of algre several inches in height. 



Barnacles (Balanus) may be said to be wholly absent— a 

 characteristic feature of this bed. A small dark coloured species 

 of mussel, of which the largest was under £ inch long, was 

 abundant in the crevices around the bases (dorsal attachment) 

 of the oyster clusters, together with a white Saxicava-like 

 lamellibranch. 



Little reliable information could be gleaned anent the past 

 history of the bed ; the people of this district do not use oysters 

 as food, and the demand from outside is too trivial to count. 

 Hence I could learn nothing as to the spawning season, but I 

 was informed by a man who occasionally collects oysters to 

 supply orders from Madras, that this bed dries up completely 

 during specially dry seasons and that the whole of the oysters 

 then die off. Subsequently I learned that May to June 1905 

 was an unusually dry season, and as the bar was closed during 

 these months the level of water in the lake receded to an extent 

 that has not since recurred ; that the whole of the lake bottom 

 between the islands of Yenadu and Irakam on the one side and 

 the east shore line on the other, became dry and that the only 

 parts left with water were the canal channels and the deeper 

 stretches west and south of Venadu and Irakam. 



I am satisfied from this evidence and from some other 

 considerations that at least the main mass of oysters forming 

 this bed in the early part of 1905 perished during the dry season 

 of that year, and that the present generation dates from a spat- 

 fall subsequent to that catastrophe. The dimensions of the now 

 existing generation are roughly those we find in European 

 oysters of four to five years of age, but I consider we are fully 

 justified in assuming them to be not more than three years old at 

 the present date (September 1908). An ample food supply and 

 freedom from the restraint upon growth imposed by the low 

 temperature of European winters will account for their size 

 being so superior to that of three- years-old European oysters. 



