Ostrea sp. (Linnaeus)
Ostrea mesenterica (Morton)
Ostrea falcata (Morton)
 

The “U” shape of Ostera mesenterica and the scalloped edge make this Cretaceous oyster easy to identify. The average size of  O. mesenterica is under an inch and is a common find in NJ. Specimens are normally found as either an upper or lower valve, although complete shells are not uncommon. The plications which make up the scalloped edge can range from 4 to 10. A less common species, Ostrea falcate is almost exclusively found as an internal cast or mold. O. falcate is a larger shell and is marked with 7 to 10 deep plications which extend nearly to the top of the shell..

The “U” shape of Ostera mesenterica and the scalloped
edge make this oyster easy to identify.
Scale 1 inch
Monmouth County, NJ

Ostera mesenterica is a smaller shell averaging
 less than one inch.
 

Ostrea falcate averages over an inch with deep plications
which extend to the top of the shell.
These are almost always found as internal molds.
Monmouth County, NJ
 
 

This scan gives a good idea of the size and differences in the plications