HEIGHT IN INCHES 



6 8 10 12 14 16 18 20 



HEIGHT IN CENTIMETERS 



55 days in running sea water in the laboratory. 

 During this time they fed actively and had con- 

 siderable shell growth along the margin of the 

 valves. After their removal from the shells the 

 cups were found to be covered with hard calcite 

 deposits on the sides facing the mantles. No 

 chalky material was found on cups or on the sur- 

 face of valves adjacent to the area of insertion. 

 On the other hand, conspicuous chalky areas 

 were formed along the edge of the shell in places 

 where the opposing valves were in close contact 

 with each other (fig. 40). It is clear from these 

 observations that the detachment of the mantle 

 from the inner surface of the shell does not result 

 in the deposition of chalky material and that such 

 deposits may be laid in the narrowest space of 

 shell cavity where the two valves touch each other. 

 Suggestions that challiy deposits result from 

 secondary solution of calcium salts of the shell 

 (Pelseneer, 1920) or that their formation is 

 somehow related to the abundance of calcareous 

 material in the substratum (Ranson, 1939-41, 



Figure 38. — Shell area in cm.' plotted against height of 

 shells in cm. Inch scales are on top and on the right. 



100 

 90 

 80 

 70 

 60 



'% 50 

 o 



< 40 

 UJ 



q: 

 < 



30 



20 



1 



J 1 I I I I I I I I I I I I III 



4 5 6 7 8 9 10 



HEIGHKcm) 



20 



30 



Figure 39. — Logarithmic plot of shell area against shell 

 height. 



zA. d. 



Centimeters 



Figure 40. — Chalky deposits (ch. d.) on the newly 

 formed shell at the edge of the valve, and near the 

 muscle attachment. 



MORPHOLOGY AND STRUCTURE OF SHELL 



33 



