tridacna, n. [L., pl., a kind of oysters, fr. Gr. eaten at three bites, tri- + to bite.].
A genus of very large marine bivalve shells found on the coral reefs of the Indian and Pacific Oceans. One species (Tridacna gigas
) often weighs four or five hundred pounds, and is sometimes used for baptismal fonts. Called also paw shell
, and fountain shell
. [1913 Webster