Thanks Andy! Wow! What a wealth of information! I think part of your post may answer my question re: Personidae/Distorsiidae. I'll have to reread it more carefully to be sure. Any thoughts on where Potamididae came from? As far as I know there is not, nor has there ever been an extant genus Potamida (or Potamidus/Potamidum). Could it be this family was named after a fossil genus? Regards, Paul M. Response to Kurt's last post, to avoid an extra posting by me: Why break them? Couldn't resorption be determined by x-raying the shells?