\Mac"tra\, n. [NL., fr. Gr. ? kneading trough, fr. ? to
knead.] (Zo["o]l.)
Any marine bivalve shell of the genus {Mactra}, and allied
genera. Many species are known. Some of them are used as
food, as {Mactra stultorum}, of Europe. See {Surf clam},
under {Surf}.