The Collaborative International Dictionary of English v.0.48:

Spur-shell \Spur"-shell`\ (sp[^u]r"sh[e^]l`), n. (Zool.)
   Any one of several species of handsome marine gastropod
   shells of the genus Trochus, or Imperator. The shell is
   conical, with the margin toothed somewhat like the rowel of a
   spur.
   [1913 Webster]