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.
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