_L_ 



Centimeters 



Figure 34. — Left valves of the two large C. inrginica from Narragansett Bay, R.I. On the right is a "normal" oyster; 

 its shell curves to the left. On the left side is an inverted oyster; its shell curves to the right. 



Most of the oysters from tlie North Atlantic and 

 Chesapeake states were taken from bottoms on 

 which oysters are regularly planted for cultivation. 

 There are no significant differences in the mean, 

 mode, and median of the two groups (table 1). 

 Contrary to the conditions found by Crozier in 

 Dosinia discus, the "index of shape" of C i^ir(iij}ica 

 is highly variable. 



SHELL AREA 



Information regarding the approximate area 

 of an oyster shell of known height may be useful 

 to oyster growers who want to determine in ad- 

 vance what percentage of tlie bottom area set 



Table 1. — Index of shape (heiiihl+ width) of oi/siers taken by 



length 

 commercial fishery 



aside for planting will be covered by oysters of 

 known size. Since the oystermen usually know 

 the number of oysters of various sizes needed to 

 make up a bushel, the information given below 

 may be used in determining in advance whether 

 the area of the bottom is sufficient to provide space 

 for their additional growth. 



It is self-evident that the area of the valve in- 

 creases proportionally tc the increase in its linear 

 dimensions. For determining the area a piece of 

 thin paper was pressed against the inner surface 

 of the right (flat) valve and the outlines were 

 drawn with pencil. The area was measured with 

 a planimeter. The outlines of small shells were 

 placed over graph paper and the number of milli- 

 meter squares counted. 



The relationship between the height and shell 

 area (fig. 38) is represented by an exponential 

 curve of a general type y=ax'' which fits many 

 empiriciil data. The y in the fonnula is the shell 

 area, and the x is the height. The parabolic 

 nature of the curve is demonstrated by the fact 



30 



FISH AND WILDLIFE SERVICE 



