these salts in the shells after thorough washing 

 with sea water of greatly variable salinity. The 

 percent of silica, aluminum, and iron, which are 

 also higher than in the analyses of shells of Hve 

 oysters, is at least in part influenced by the 

 efficiency of plant operations in removing mud 

 from the surface of the shells. 



Chemical composition of shells of 0. edulis is 

 not significantly different from that of C. virginica. 

 Table 8 gives the results obtained by European 

 scientists. The data quoted from various sources 

 are taken from Vinogradov (1937). 



A nmch more detailed analysis of dead oyster 

 shells dredged from the bottom of Galveston Bay 

 8 miles east of San fjeon was made recently by the 

 Dow Chemical Company (Smith and Wright, 

 1962). The shells were scrubbed in tap water 

 with a nylon brush, rinsed in distilled water, dried 

 at 110° C, and ground in a porcelain mortar. 

 With the kind permission of the authors the 

 results are given in table 7. Additional 19 ele- 

 ments were sought but not found at the following 

 sensitivity limits: 



10 p. p.m. — arsenic, barium. 

 1 p. p.m. — antimony, chromium, cobalt, ger- 

 manium, gold, lead, lithium, mercury, 

 molybdenum, nickel, vanadium, and 

 zirconium . 

 0.1 p. p.m. — beryllium, bismuth, cadmium, 

 silver, and tin. 

 The authors remark that traces of clay entrapped 

 within the shell may have influenced the findings 

 for titanium, manganese, copper, or zinc; and 

 that individual variations in silicon, iron, and 

 aluminum were due to contamination not remova- 

 ble by washing. It appears feasible that these 

 variations may have been caused by spicules of 

 boring sponges and algae infesting the shells. 



Table 7. — Composition of C. virginica oyster shell dredged 

 from Galveston Bay, according to Smith and Wright 

 (1963) 



Table S. — Chemical composition of shells of O. edulis (in 

 percent of ash residue) 



According to Creac'h (1957), all shells of 0. 

 edulis and C. angulata contain traces of phos- 

 jjhorus. The French biologist found that the 

 pliospliorus content is variable. Expressed as 

 P2O3, it varies in C. angulata from 0.075 to 0.114 

 percent. There is a significant difference in the 

 phospliorus content in various parts of the shell. 

 The amount of phosphorus per unit of volume nf 

 shell material is lower in the chalky deposits than 

 in the hard portion of the shells. Thus, in laying 

 a chalky deposit the moUusk utilizes from 2.4 to 

 2.6 times less phosphorus than is needed for 

 secreting the same volume of harder shell 

 substance. 



Tlie presence of small quantities of strontium 

 in calcareous shells of mollusks is of particular 

 interest because of its apparent relation to arago- 

 nite. The marine organisms containing calcium 

 carbonate as aragonite have relatively higher 

 strontium content than those liaving calcite shells. 

 The relationship between the two elements is 

 expressed as strontium-calcium atom ratios 

 (Thompson and Chow, 1955; Trueman, 1944; and 

 Asari, 1950). In C. nrginica and C. gigas the 

 strontium-calcite ratio x 1,000 varies l)etween 

 1.25 and 1.29. Ostrea lurida from California has 

 a lower strontium content, the ratio being 1.01. 

 The percentages of Ca, Sr, COo, and organic matter 

 in the shells of three species of oyster and in Mya 

 arenaria, in wliich the content is the highest 

 among the bivalves, given by Thompson and 

 Chow (1955), are summarized in table 9. The 



Table 0. — The percentage of calcium and strontium in the 

 shells of oysters and soft shell clam 

 (According to Thompson and Chow, 1965] 



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FISH AND WILDLIFE SERVICE 



