What is the meaning of Aphrodite's symbol the scallop shell?

Some versions of the birth of Aphrodite have her washing onshore on a large scallop shell. "Botticelli's Birth of Venus" is an example of this motif/story. The scallop shell may also refer to the female genitals, as the ancient Greek Word for scallop, kteis, may mean either. "Laughter-loving" Aphrodite undoubtedly smiles at the double entendre.