Hi, All!
       Since several people have picked up the Chesapecten topic, I thought I might add some more information.  My specimens show considerable variation.  They begin with young shells - 2 inches and under - which are light beige, very scaley  (spelling, my ability to spell seems to be decreasing with my age?) , sand filled, and extremely fragile.  Older specimens vary from a right valve that is darker beige and alnost looks like alabaster, some scaling remaining to dark gray valves which are a lot tougher but have lost their scales.  All of these are definitely Chesapecten, and they are Miocene.
I have one complete shell which is all beige, required some coating of the inner surface with acrylic to toughen it before I could clean the outer surface and measure about 3 - 4 inches.  My largest is a good 6 inchese, was fragile on the edges, retains some scaling, and varies from beige to darker gray.  These are all from the same site, age Miocene.
        Would differences indicate some time variation, or just variations in the trace minerals in the ground water affecting parts of the collectig area.  I am fairly certain that they come from a sandy cliff above the beach, as walking along the beach is necessary to get to the site.  I am not the finder of these shells, so I will lleave it to the finder if he wants to reveal himself.   I doubt that he would want to be inundated with requests, as the site is hard to reach; I couldn't negotiate it in my present condition.
        I think that anyone really into the Pectinidae eventually becomes interested in the fossils.  I don't have enough of the above species yet to trade, but I might have extant species to trade for fossil ones.
                        Cheers!
                                  Linda W. B.