Concave holes are drilled by Naticidae, wile tubular ones are by Muricidae.
The drilling process is not the same for the two groups.
You should consult the book:
V. Fretter & A. Graham: British Prosobranch Molluscs: their functional
anatomy and ecology. The Ray Society, 1994 London pp 1-820
Regards
Enzo Campani
PS.
Marry Christmass and Happy New Year to all the gang there.
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