I believe "Pecten glabra" or "Chlamys glabra" is a misspelling of Pecten
glaber (Linne, 1758).  However, I am amazed at how often "glabra" is used.
Perhaps there is some disagreement over the correct spelling??  I have also
seen fossil specimens labeled "Chlamys glabra".  I don't know whether these
actually are a different form, or are just fossil Pecten glaber.

Paul M.