lithodomus

from The Century Dictionary.

• noun A genus of mussels of the family Mytilidæ, of small size and subcylindric form, which burrow in rocks, and are known as date-shells. L. lithophagus is an example. Also called Lithotomus and Lithophagus. See cut under date-shell.
• noun [l. e.; pl. lithodomi (-mi).] A member of this genus.

from the GNU version of the Collaborative International Dictionary of English.

• noun (Zoöl.) 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.