ID Help for tiny triangular shell, florida

[paleogirl]

I regularly recover tiny triangular shells (bivalves?) at archaeological sites on the gulf coast of Florida. No one seems to be able to ID them. Can someone help? Size is about 1 cm long and .5 cm wide. I can't seem to upload a photo, so, here is a link to the photos online.
https://picasaweb.google.com/10690594991...directlink

If you need more information, please let me know. I would really like to find out what these are. It is driving me crazy.

Thank you for any help you can give.