I found these little clams on a bug hunt at a retention pond near my house. These little buggers look like bits of quartz gravel and if I hadn't been trolling the mud for bugs, I'd never have noticed them at all. The biggest ones aren't even 1/8th of an inch wide. They seem to be almost perfectly symmetrical. The shell surface is smooth, glassy and gives a high shine, again much like quartz gravel. Any guesses on which species this might be?