143 



The varying forms of the valves in the following table (and for other 

 species in other tables of this article) are largely due to the distortion of 

 the beds in which the fossils are preserved. This variation is corrected 

 by the average. 



VALVES of Obolus Bretonensis from Assise E 3 d. (one from E. 3, a.) 



Dimensions 

 &c. of the 

 valves. 



