CYTHEREA 



pally to the tertiary formations, being not unfrequent in 

 the Calcaire grossier and the London Clay j they occur also 

 in the green sand, and in some of the secondary beds. 

 Many of the recent species are very beautiful^ and natu- 

 rally highly polished, and some are remarkable for pointed 

 spinous processes on the outside (e. g. CDione, Lam., Venus 

 Dione, Linn.) They are found in the seas of all coun- 

 tries, but particularly in the East and West Indies : in 

 Japan the valves of C. lusoria are gaily painted and gilt 

 on the inside, and they are then used for games of chance 

 or skill, as our playing cards. 



