razor shell 
noun
A burrowing bivalve mollusc with a long slender shell which resembles the handle of a cut-throat razor. Also called jackknife clam or razor clam in North America.
- Family Solenidae: Ensis and other genera.
- The middle regions of the beach are surf-beaten, but the sheltered southern corner, at low tide, reveals fine sands thickly populated with razor shells, tellins, surf clams and sand mason worms.
- Other prey, such as bristle worms, razor shells and tellins are also taken when available.