Description: The upper valve is highly convexed while the lower valve is not as convexed. Both valves are marked with between 8 to 10 sharp angled plications. The upper valve curves downward over the hinge and ends in a hole or foramen where in life a muscle attached the shell to the bottom of the sea floor.  The hinge is straight.  Both valves may have faint concentric growth lines that cross the plications.  They appear to be circular to oval in outline.

Commonality: Choristothyris is the only brachiopod that is commonly found in moderate numbers in the oyster beds of the Navesink formation at Big Brook.

Similar fossils: Both valves are very distinctive and are hard to confuse with any other shell. Even fragments are identifiable.

Size: These brachiopods are usually small, never exceeding 1 to 1.5 cm (about .5 in) long and wide.

Notes: Unlike the oysters, when this brachiopod died, the muscles that opened the valves would contract thus closing them together. So it is very common to find them articulated in situ.

In New Jersey, this brachiopod is a fairly good indicator of the Navesink formation.
Brachiopod
(Brachiopoda)
Choristothyris plicata Say
Upper valve of
articulated specimen
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Lower valve of
articulated specimen