Miocene Mystery Shell

[I_gotta_rock]

Okay, here's a weird one for any shell people out there. Found this on the Potomac's beach where the cliffs have Eastover, St Mary's and Choptank FM exposures. At first, it was a blob of clay with what looked like a hinge showing at one end. I chalked it up to oyster or mussel. Brough it home, cleaned it up most of the way and said, "What the heck?" The texture is really strange. It's convex where I would expect it to be concave. It's lumpy, but not heavily sculptured. I took it to some people who were more familiar with the spot and/or knew something about vertebrates, in case my mollusk assessment was totally off. No, looks like invertebrate of some kind, they said. I've identified and catalogued over 70- species from the cliffs, pouring over the same references for countless hours. There are a few approximately the right shape, given how broken it is, and have similar parallel growth lines, but the texture and lumps???? And that weird ridge 1/2 of the length from the beak? Multiple shells overlapping? Again I say, "What the heck?"

[Al Dente]

Maybe Atrina or some other Pinnidae genus. I think the ridge was formed by compaction that deformed the shell.

[I_gotta_rock]

8 minutes ago, Al Dente said:

Maybe Atrina or some other Pinnidae genus. I think the ridge was formed by compaction that deformed the shell.

Yeah, that was one of my possibilities. Even if it turns out to be a deformed, mangled specimen of something, I think I'm going to keep it for the geological story it holds.