Figure 42. — Four arbitrary quadrants of the inner surface 

 of shell used for estimating the distribution and extent 

 of clialky deposits. 



Atlantic Coast from Long Island Sound to Georgia. 

 Nearly one-half of the total number of valves 

 examined (48 percent of left and 53 percent of 

 right valves) were free of the deposits. (The 

 percentage of oysters without chalky deposits 

 was not determined because in many shells of the 

 collection the valves had separated and could 

 not be arranged in pairs.) In about 25 percent 

 of the total number of shells the chalky deposits 

 cover less than one-quarter of the valve area. 

 Larger deposits occurred in diminishing number 

 of shells; those covering more than three-quarters 

 of available space (class 4) comprised less titan 

 3 percent of the total number examined. 



There was no particular area on the valve 

 surface where chalky deposits were formed more 

 often than in any other place. The differences 

 in the frequency of their occurrence in different 

 quadrants of a valve were not significant. 



In 0. edulis, according to Korringa, chalky 

 deposits form more often in deep (cupped) shells 



Table 3. — Percent of valves of C. viruinica with chalky 

 deposits 



than in flat ones and can be found principally in 

 the area in front of the cloaca, cjuadrant V accord- 

 ing to our terminology. i\o such differences in 

 the place of formation or in the type of shell 

 could be observed in C. virginica. 



From the observations on oysters of Prince 

 Edward Island, Medcof (1944) concluded that 

 chalky deposits are normal parts of shells and 

 that they have "functional importance" in pre- 

 serving "a size relationship between meats and 

 shell cavity" and hi regulating "the curvature of 

 the inner face of the shell throughout the oyster's 

 life." There could be no argument about the 

 first conclusion that chalky deposits are normal 

 parts of the oyster shell. The fact that they 

 appear during the first weeks of the oyster's life 

 confirms this statement. The second conclusion 

 that they preserve the curvature of tlie shell is 

 unpossible to prove without careful study of a 

 large number of shells. In comparing the con- 

 tours of the shells of New England and Chesapeake 

 Bay oysters with and without chalky deposits, 

 I failed to notice any significant difference between 

 the two groups. 



Japanese investigators (Tanaka, 1937, 1943) 

 found great variability in tlie distribution of 

 chalky deposits in C (jigas and C. futamiensis. 

 Large porous areas may be found in the shells 

 of these species near tlie anus, in front of the 

 labial palps, or near the gonads. There seems 

 to be no evidence that they occur primarily in 

 one particular place of the valve. These obser- 

 vations agree with my observations on C. rirginica. 



CHAMBERING AND BLISTERS 



The French word "chambrage" or chambering 

 has been used by European biologists to describe 

 shallow cavities, mostly in the cupped valves of 

 0. edulis. The cavities are usuallj' filled with sea 

 water and putrified organic material. In the 

 museum specimens these spaces are dry and filled 

 with air. Sometimes only one chamber is found, 

 but occasionally an entire series of cavities may 

 be present. The chambers may be invaded by 

 tube-forming annelids living in the oj'ster (Houl- 

 bert and Galaine, 1916a, 1916b). The successive 

 layers of shell material in the chamber are not in 

 contact with each other but surround an empty 

 space. This gives the impression that the body 

 of the oyster had shrunk or retracted and occupies 

 only a small portion of shell space. This view is 

 generally accepted by European oyster biologists 



35 



