Telescope-shell Creeper or Mud Whelk

Notes:

We saw several of these large snails with long, heavy conical shells (almost as long as my hand) on the tidal sand flats at Poverty Point in the Great Sandy National Park. The fourth shot shows an uninhabited shell. Thanks to auntnance123 for assistance with the ID. There is not a great deal of information to be found online about these snails - it seems that they are reasonably common throughout 'tropical northern Australia' so I think these ones must be right on the south edge of their range.