> about 5-6mm the muricid had to bore. Patience pays off! (and the
> only
> large muricids in most of these localities are Typhis, so I guess
> these must be the culprits).

Of course molluscs with shells are not the only molluscs which bore holes
in shells.  From what I have seen modern day octopus make small
cylindrical holes in the spires of univalves.  Perhaps there was an
extinct species of octopus or something else that was responsible.

Andrew D