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Invertebrate Fossils OF NJ

Pycnodonte convexa (Say)
aka Gryphaea Convexa

 The oysters 5 6 Exogyra and Pycnodonte were the most common bivalves of the Cretaceous period. Lying on the seabed floor with the convex side in the mud and the flat side positioned at the seafloor surface for camouflage. Pycnodonte convexa is strongly convex on the lower side and concave on the upper, with a lobe like extension to one side. This shell may be as wide as it is long and is most often found with drill holes from the boring sponge Cliona cretacica. This species is quite common, often found in large numbers where the shell beds are exposed along the stream banks. The vast majority of these oysters are found with the original shell intact with a few locations producing internal casts.



This specimen is a little over 3 inches
The lobe like extension can be seen on the left in this picture



Pycnodonte convexa lower side
Monmouth County, NJ



These shells are prone to breakage along the growth lines.
This is a complete specimen, 2 3/4 inches long by 3 1/4 inches wide.
Note the bore holes in the top of the shell.



The upper valve is concave with concentric growth ridges.  



Internal cast of Pycnodonte convexa.
Note the large muscle scar, this is where the muscles used to
open and close the shell would have anchored to the shell. 

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