It is a Baler shell, so named because it was used for baling out canoes in the tropical Pacific and as a water carrier in Australia.
Sometimes it is called a Melon shell.
A common Australian species of baler is Melo amphora. It's very variable - the spines can get worn off in older specimens. I can't tell you certainly if yours is that particular species as I'm not well versed in the group, but the light band is right for it. Try Googling Melo and see what comes up.
It has a very big foot with which it smothers large bivalves and forces the valves apart. Then it rips out the flesh with its radula (tongue armed with lots of teeth).