The Collaborative International Dictionary of English v.0.48:

Lithodomus \Li*thod"o*mus\, n. [NL. See Lithodome.] (Zool.)
   A genus of elongated bivalve shells, allied to the mussels,
   and remarkable for their ability to bore holes for shelter,
   in solid limestone, shells, etc. Called also Lithophagus.
   [1913 Webster]

   Note: These holes are at first very small and shallow, but
         are enlarged with the growth of the shell, sometimes
         becoming two or three inches deep and nearly an inch
         diameter.
         [1913 Webster]