The general consensus is that the species is Cypraea xanthodon, now correctly known as Erronea xanthodon(see link below). This species is known to occur as far south as Sydney, but a specimen as far south as Bermagui is, indeed, unusual.
Though it is a pretty shell and you probably want to keep it, if you could bear to part with it, it would be a valuable addition to our collection given the considerable range extension.
Dr Mandy Reid
Collection Manager, Malacology Australian Museum”