lo March, Morphogenesis of certain Pelecypoda. 



The shape of the animal accentuates the curve of the 

 growth lines. The flatness of the valves brings this curve 

 entirely on to the laterally-faced part of the flank, as there 

 is no anteriorly-faced part for them to run upon. The 

 diagonals get the full benefit of the marked up-curve, 



Fig. 8a. 



Showing the efiecl of growth lines similar to those of T. dadalea 



on diagonals. 



because they are continued to the anterior edge of the 

 valve. 



The effect of growth lines, similar to those of 

 T. dcsdalea, on diagonals is seen in Fig. 2>a. The up- 

 curve becomes marked about the middle of the flank. In 



