Sundial shell

from The Collaborative International Dictionary of English v.0.48

Sundial \Sun"di`al\, n.
   An instrument to show the time of day by means of the shadow
   of a gnomon, or style, on a plate.
   [1913 Webster]

   {Sundial shell} (Zool.), any shell of the genus Solarium. See
      {Solarium}.
      [1913 Webster]