Ever since I’ve figured out what they were, local Pinnid fossil specimens are a personal favorite to find. In examining the remaining shell material in these fossils, I have been able to see the prismatic layer represented on the shell hinge in at least two specimens. The specimens below show the detail.

The layer in a specimen from May 30th, 2019

The layer from Sea Pen III (Likely a species of Meekopinna)

Further Reading