Wednesday, May 2, 2012

Exogyra costa from the Navesink Formation

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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