Thaks Mike and others who have replied on this matter.  However, i am
refering to worm tubes resulting from the worms burrowing into the
shell, which often leaves a dark trace visible under the surface - not
to attatched calcareus tubes.  What i'd like to know is how often worms
actually burrow into the shells of live Cones, leaving this dark mark
just under the surface of the shell.

Thanks,
Ross.