123 
Such are said also to be found at Devizes and Blackdown, 
with the upper valve. It is possible that these are different 
species from those in the Chalk, the costz are less prominent, 
and the striae more distinct; at present, however, I can 
consider them only as varieties. 
Tab. 56, Fig. 3 represents a specimen in ferruginous 
Sandstone from Chute, which may possibly prove to be a 
distinct species. Its length exceeds its breadth by one- 
fifth, and on the sides of the larger cost are two lesser 
ones, which are partly blended with them; the surface is 
nearly smooth. I have only seen this specimen. 
