Another common oyster in the Navesink formation is Exogyra costa. This can be distinguished from other oysters by the curled shape of the shell and presence of a wrinkled surface. Some of these shells can get very large, approaching six inches across.
Left valve top
Left valve anterior
Left valve, left side profile
Left valve posterior
Left valve, right side profile
Left valve interior
The right valves are layered and slightly turned up at the edge so that they look a little like a topographic map when viewed.
Right valve top
Close up of the surface layering
Right valve interior
Right valve posterior
These specimens were found at Big Brook near Marlboro, New Jersey in the Navesink formation which is upper Cretaceous (Maastrichtian stage) in age.
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