Its is even smaller than that, since it is not a clam but a Queen Scallop she sits in, which never get as big as the larger clams, which can reach three feet or more. You can perhaps see why, Aphrodite, born from the foam that resulted when the testicles of the castrated Cronus were thrown into the sea, comes ashore on a scallop shell. Because if you hold the shell with the outside facing you, and the hinge part to the bottom, you can see what looks very like a mount of Venus at the bottom. Fun if you like that sort of thing.

In Christian tradition it was the symbol of St James, though they turn it the other way up. In case anyone gets the wrong idea perhaps.