The Collaborative International Dictionary of English v.0.48:

Dimya \Dim"y*a\, Dimyaria \Dim`y*a"ri*a\, n. pl. [NL., fr. Gr. ?
   = ? + ? to close.] (Zool.)
   An order of lamellibranchiate mollusks having an anterior and
   posterior adductor muscle, as the common clam. See Bivalve.
   [1913 Webster]