razor shell

from The Century Dictionary.

• noun The shell of a razor-fish; a bivalve mollusk of the genera Ensis, Solen, or Siliqua: so called from the shape of the shell, which resembles a razor. Compare razor-fish, 3.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A bivalve mollusc, of genus Ensis, having a long, straight shell, that burrows in the sand.