Tridacna \Tri*dac"na\, n. [L., pl., a kind of oysters, fr. Gr. ?
eaten at three bites, ? tri- + ? to bite.] (Zool.)
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] Tridactyl