Source : Webster's Revised Unabridged Dictionary (1913)

Sea clam \Sea" clam`\ (Zo["o]l.)
   Any one of the large bivalve mollusks found on the open
   seacoast, especially those of the family {Mactrid[ae]}, as
   the common American species. ({Mactra, or Spisula,
   solidissima}); -- called also {beach clam}, and {surf clam}.