107 



The following table will show the size and salient characters of this 

 species. The second, third and fourth columns give the dimensions of 

 the valves ; the fifth column, the length of the callus, in front of or near 

 which the central muscles are placed ; the sixth column shows the dis- 

 tance from the uinbo of the principal growth furrows on the outer sur- 

 face of the valve, which mark resting stages in the growth of the shell, 

 the main furrow is usually at the front of the visceral cavity ; the 

 seventh column indicates the height of the hinge area ; and the eighth 

 column the space between the impressions of the vascular trunks. 



DIMENSIONS of Leptobolus atavus from A.ssise E. 3 e. 



Dimensions 

 and features 

 of the valves 



