Table 5. — Chemical composition of oyster shells in percent 

 of shell weight 

 [From Hunter and Harrison, 1928] 



20 300 40 



SHELL AREA, cm^ 



Figure 51. — The relationship between the area of muscle 

 scar and the area of the shell of C. virginica. 



dorsal half of each valve is the imprint of a 

 vestigial muscle in the mantle, discovered in 1867 

 by Quenstedt in the valves of the early Jurassic 

 oyster, Gnjphaea arcuata Lamark, and found by 

 Stenzel (1963) in C. virginica. In my collection 

 of living C. virginica the imprint is hardly visible 

 (figs. 15, 21, and 22). Slight adhesion of the 

 mantle to the valve indicates the location of this 

 area which Stenzel calls "imprint of Quenstedt's 

 muscle." 



SHELL AREA-MUSCLE ATTACHMENT AREA 



Figure 52. — Frequency distribution of the ratio of muscle 

 scar area vs. shell area in the shells of C. virginica of 

 Atlantic and Gulf States. 



' Loss above 110° C. Ignited. 



 Loss to 100° C. 



' Average for samples 1 and 2. 



CHEMICAL COMPOSITION 



The oyster shell consists primarily of calcium 

 carbonate, which composes more than 95 percent 

 of the total weight of the shell. The balance is 

 made up by magnesium carbonate, calcium sul- 

 fate, silica, salts of manganese, iron, aluminum, 

 traces of heavy metals, and organic matter. 

 Several analyses of oyster shell found in the 

 literature are incomplete, particularly with refer- 

 ence to trace elements. Analysis made for the 

 U.S. Bureau of Fisheries by tlie Bureau of 

 Chemistry of the Department of Agriculture and 

 published in 1928 (Hunter and Harrison, 1928) is 

 given in table 5. 



Dead oyster shells buried in tlie mud of the 

 inshore waters of Texas and Louisiana are exten- 

 sively dredged by commercial concerns primarily 

 for the manufacture of chicken feed. Analysis of 

 these shells as they are received at the plant after 

 thorough washing in sea water is given in table 6. 



The calcium carbonate content of these shells is 

 probably lower than in live oysters due to their 

 erosion and dissolution of lime in sea water. 

 The chloride content is affected by the retention of 



Table 6. — Chemical composition of mud shells received al 

 the plant of Columbia-Southern Corporation at Corpus 

 Christi, Tex. 



[Percent of constituents in samples dried at 110° C.) 



(.Analysis supplied by Columbia-Southern Corporation and copied with 

 their permission.) 



MORPHOLOGY AND STRUCTURE OF SHELL 



43 



