Crocea will not get that big...they are one of the smallest in the tridacnid family. It's got to be a derasa..and a purdy one at that.

One thing to keep in mind when making a clam ID is that although the scutes can be a somewhat reliable variable in helping to make an ID, they are not to be considered a 100% tell all sign.

Some clams, if wild harvested, can be completely smoothed out by way of the grinding action as they burrow into rock. You may see no ridges or lines at all! On the other hand, other clams that you would imagine to have subdued scutes (like crocea) yet are farm raised and never truly got to be a "boring clam" may have exaggerated scutes.

Finally, there are clams that have been known to hybridize...I've seen some BEAUTIFUL Squamosa X Derasa that would knock your socks off.

Got to love Knopp's "Giant Clams" book...it's one of my most read, and re-read books. If you own or want to own a clam, you too should own the book

D