226 DESCRIPTIONS OF THE BOGNOR FOSSILS. 
and the opposite edge straight, converging towards the anterior extremity ; pos- 
terior extremity semicircular. 
Occurs in masses of Septarium. It is like Modiola depressa of Min. Con. t. 8, 
but is more pointed. 
Pinna margaritacea. 
This appears to have sharper ribs than P. affinis, but probably they are the 
same species differently preserved. 
In Septaria. 
CONCHIFERA MONOMYARIA. 
Ostrea cariosa. 
The structure of the shell of this species, noticed by Deshayes, is common to 
others, even to the recent O. edule. It is the constant cellular structure of the 
mass between the external fibrous lamine and the pearly lining of the shell, and 
is manifest in old shells when partially decayed: it much resembles the cellular 
tissue in the bark of trees, or fat between the muscles of animals. 
Ostrea tabulata. 
Spec. Cuar.—Shell orbicular, depressed, smooth ; upper valve slightly con- 
cave, even, its plates few, with distant, scarcely raised edges; lower valve 
obscurely marked by radiating undulations, its plates few, in groups, with 
remote, deeply imbricating edges; beaks small, pointed ; muscular impression 
ovate, curved, of a moderate size. 
This was evidently a rapid-growing shell; its nearly smooth external laminz 
extend far between each period of growth and show their fibrous structure di- 
stinctly, especially upon the surface. An abundant shell. 
Ostrea elephantopus. 
This Oyster does not properly belong to Bognor, as it is only found at some 
distance from the rocks, and is probably recent on the opposite side of the 
Channel. 
MOLLUSCA GASTEROPODA. 
Infundibulum trochiforme. (Tab. XIV. fig. 27.) 
Larger specimens occur at both Bognor and Barton. I cannot rest satisfied 
