There's a wierd late Cretaceous bivalve occurring rarely in the tuffs
on Pitt Island (one of the Chatham Islands) about 800km off the east
coast of NZ's South Island.

The best specimen I have seen is one I collected a few weeks ago;
none that I have knowledge of are complete. The unattacjhed valve is
I believe unknown. Mine is missing the posteroventral corner
(assuming that the attached valve is the right one) and the
hingeplate.

The characters present indicate that it's a spondylid, but most
certaionly it's not Spondylus. There is nothing like it in any
literature I have seen, including Treatise of Invertebrate
Paleontology.

If anyone thinks they can help, or knows someone who might be able
to, I can send images.