160 MADRAS FISHERIES BULLETIN [VOL. XVI, 



made in 1885, 31 in 1887, 7 (!) only in 1889. On theKarai Karuwal 

 Par, one of the most frequently productive of the Indian banks, a 

 sorry seven dives sufficed for the examination of 1888, while the 

 Velangu Karuwal Par had 74 dives in 1887 and 63 in 1891. 



(2) The average weight and dimensions of an average sample 

 of the living oysters found in each locality should be recorded with 

 exactitude. Where the oysters are numerous, the sample should 

 be as large as possible to diminish the possibilities of error. The 

 weight should be recorded in pounds, ounces, and drams, and 

 where possible 100 oysters should be weighed together. In express- 

 ing the average weight of the individual oyster it might be useful 

 to express the result in grammes, as the metric system is more con- 

 venient for the purposes of comparison than avoirdupois weight. 



When there are large numbers of oysters present and pos- 

 sibilities of an eventual fishery, the cleaned (empty) shells of 5 

 individuals should be averaged in like manner. 



I think it probable that we shall eventually find the average 

 weight per shell the most reliable guide in ascertaining whether 

 growth be satisfactory or not and also in ascertaining the approxi- 

 mate age of oysters of unknown history. 



In the same way I recommend the dimensions to be recorded 

 in centimeters and millimeters, recording the length, depth, and 

 thickness of 25 individuals taken haphazard and without selection 

 from the samples brought in by the clivers. 



The length is the greatest horizontal distance between the 

 anterior and the posterior margin of the shell taken parallel with 

 the hinge-line, as shown upon the accompanying diagram. The 

 depth is the longest line that could be drawn (measured) at right 

 angles to the line of greatest length ; it extends from the hinge to 

 the most ventral point of the free margin of the shell. 



The anterior aspect of the shell can readily be distinguished as 

 such because of the presence of the byssus at that side. 



The thickness should be measured by means of a pair of calli- 

 pers, clasping the jaws upon the thickest part of the oyster, a point 

 indicated in the diagram on the next page by the letter A. 



(3) The general outward appearance, stunted or of free vigorous 

 growth, should be stated and also whether the oysters be exten- 

 sively covered or not with sponges and other crusting organisms 

 in exceptional degree. 



