These don't have any skin on the shells, they look identical to the surf clams we use for bait for striper fishing. When if first saw them I had figured that someone had been fishing there and had shucked some clams for bait and tossed the shells in the water, but these were live and were burrowed into the bank. I picked up a few and they are alive. I've used them for bait, they sure look like clams to me. Maybe someone tossed some left over bait and they lived? It's fast moving water but not deep, the banks are muddy or sandy in most places. These are no more than few feet from shore, exposed during low tide in the river.
An old timer there said they were just freshwater clams but I wasn't sure if he was serious or being sarcastic. They're too big to be eating clams either way, and I do know what you mean by the green rays, but these are dull white/brown clam shells. I do gather mussels farther down stream where the river meets the bay, but that's 20+ miles down stream and in saltwater, those look just like the mussels you get at the local seafood buffet.
Dark in color with a pearl or iridescent look to the shell, elongated in shape.
I've never seen those anywhere but well into saltwater, but what I see up stream are clams. I can't tell those from the clams I gather on the beach at the shore for bait.
Those things are putting native mussels out of business in a big way and it's going to be a problem that most don't realize.
