Was Argobuccinum tumidum. Now tumidum is considered a subsp of A pustulosum. So I'm not sure what I have here at subspecific level.
As per normal on these wild beaches wind prohibited photography so next few postings are back of the car jobs contrived with sand I had on hand from Ahipara's giant sand dunes from the start of the week. Patarau is all boulders at high tide, but remote enough to still have pickings, most will be returned for others to enjoy.