0.3 



Millimeters 



Figure 47. — Cross section of the shell of adult C. inrginica embedded in bak(-lite and polished on a glass wheel with carbo- 

 rundum. Two upper layers consist of clialky deposits. 



after decalcification of the calcite-ostracum of 

 C. virginica shells from Long Island Sound and 

 Cape Cod waters are in agreement with those 

 given for 0. edulis. The content of conchiolin in 

 my samples varied from 0.3 to 1.1 percent with 

 the mode at 0.6 percent. For these analj'ses 23 

 pieces of shell were taken from 16 adult oysters 

 not damaged by boring sponge. The samples 

 varied in weight from 0.5 to 15 g. 



Higher percentage of conchiolin in tlie prismatic 

 layer may be expected because this layer represents 



the new growth of shell whicli lias not yet com- 

 pletely calcified. 



The role played by conchiolin in the deposition 

 of calcium salts in the form of calcite or aragonite 

 presents a very interesting problem which has not 

 yet been solved. Recent electron microscope 

 studies of pearl oyster shells made by Gregoire 

 show tliat the organic material in which aragonite 

 crystals are laid (Gregoire, Duchateau, and 

 Florkin, 1950) is arranged as a series of bricklike 

 structures. No such arrangement has been de- 



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FISH AND WILDLIFE SERVICE 



