_l_ 



Centi meters 



Figure 35. — Two upper (right) shells of old C. virginica from Chesapeake Bay (left) and Matagorda Bay, Tex. (right). 

 The direction of growth changed suddenly about 50° to the left in the Chesapeake oyster and about 75° to the right in 

 the Texas oyster. 



that the log/log plot (fig. 39) fits a straight line. 

 The numerical values of factors a and b were 

 found to be equal to 1.25 and 1.56 respectively. 

 The formula reads, therefore, y=1.25x'^^ As 

 a convenience to the reader who may be interested 

 in finding directly from the curve the average area 

 occupied by a shell of a given height, the data 

 computed from the equation can be read from the 

 curve in figure 38. The measurements are given 

 both in centimeters and inches. The data refer 

 to the random collection of live oysters from the 

 coastal areas between Prince Edward Island, 

 Canada, and the eastern end of f^ong Island 

 Sound (table 2). 



The relationship between the height and area 

 ol the upper valve of C. virginica is in agreement 

 with the findings of other investigators (New- 

 combe, 1950; Nomura, 1926a, 1926b, 1928) wlio 

 concluded that in several marine and fresh-water 

 bivalves and gastropods the dimensi'inal relation- 



ships can be adequately e.xpressed by the formula 

 of heterogenic growth, y = bx''. According to No- 

 mura's (1926a) interpretation of the growth of the 

 clam Meretrix meretrir, the constant b in this 

 fornmla represents the eff'ect of the environment 

 while k is a factor of differential growth. No- 

 mura's conclusions may be applicable to otlier bi- 

 valves, and if confirmed by further studies tliis 

 method may become useful for quantitative de- 



Table 2. — Height and shrlt area of northern oijsters com- 

 puted 1)1/ ii.itni/ thi eejiiation ;/ = l.Sox'-'''^ 



MORPHOLOGY AND STHrCTIRF, OF SHELL 



31 



