large shells, for some individuals, that appear to be of a 

 more luxuriant growth than others, are thin in the mid- 

 dle. 



Since this curious shell was discovered by M, Defrance, 

 attached to a fragment of an Inoceraraus* Cuvieri, it has 

 been repeatedly sought for; at length Mr. G. B. Sowerby 

 was fortunate enough to find the attached valve upon 

 an Echinus in Chalk ; its cellular structure was then 

 noticed as a character by which to distinguish it from 

 other attached shells, and numerous specimens have been 

 met with upon Echini, Inocerami, and other shells found 

 in Chalk, in various parts of England. The upper valve 

 had still remained unknown, had it not been accidentally 

 discovered almost concealed in chalk upon a dislocated 

 Echinus, picked uj) at Brighton several years ago, by 

 G. B. Snow, Esq. : this is shewn in the upper figure. 



The lower figure shews three states of the attached 

 valve, found upon an Echinus sent from Norfolk by the 

 Rev. G. R. Leathes, 



*This Generic nauie will probably besiipersecled. 



