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circles are needed to cover it adequately, equivalent therefore to a total of 1,200 dives. 

 From the office records I notice that in 1890, ninety dives were made ; in 1892, 158 

 dives ; in 1896, 220 dives — far too few to give a reliable conception of the condition 

 of the bank as a whole. 



Other banks fared even worse. Taking some figures at random I find that 

 12 dives were made to suffice for the Alluva Par in 1886 and 32 in the following 

 year. On the Tundu Par 35 dives were made in 1885, 31 in 1887, 7 (!) only in 

 IS 39. On the Karai Ivaruwal Tar, one of the most frequently productive of the 

 Indian banks, a sorry seven dives sufficed for the examination of 1888, while the 

 Yelangu Earuwal 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 possi- 

 bilities of error. The weight should be recorded in pounds, ounces, and drams, and 

 where possible 100 oysters should be weighed together. In expressing the average 

 weight of the individual oyster it might be useful to express the result in grammes, 

 as the metric sj stem is more convenient for the purposes of comparison than avoirdu- 

 pois weight. 



When there are large numbers of oysters present and possibilities of an 

 eventual fishery, the cleaned (empty) shells of 25 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 g-owth be satisfactory or not and also 

 in ascertaining the approximate 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 divers. 



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. 



HINGE 



DORSAL ASPECT 



POSTERIOR 

 ASPECT 



BTSSUS 



ANTERIOR 

 ASPECT 



VENTRAL MARGIN 



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 callipers, clasping the 

 jaws upon the thickest part of the oyster, a point indicated in the diagram by the 

 letter A. 



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