Freshwater friends,

Can anyone take an easy guess what the common triangular clam is that
inhabits the lakes of North Carolina? It has coarse concentric ridges on the
exterior.

I just found a dead pair with a couple of live limpet-shaped gastropods
(Ferrissia?) at Lake Gaston in Virginia near the NC border. I understand the
lakes around here are all man-made because glaciation did not occur. The
triangular clam is most likely an import. No?

David Kirsh
Durham, NC