The Collaborative International Dictionary
Sea clam
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 solidissima or Spisula solidissima); -- called also beach clam, and surf clam.
Wiktionary
sea clam
n. The Atlantic surf clam, (taxlink Spisula solidissima species noshow=1).