I don’t see any drill holes in these specimens. If you are referring to the hole in the top of Diodora chipolana carolinensis that is a feature of species in the Family Fissurellidae aka the key hole limpets. These marine gastropods strongly attach to hard substrates and allow water to enter under their shells and over their gills forcing exhalent water and bodily wastes out through the hole at the top of the shell.