Elephant Shark Egg Case
Found on Brighton Beach in Melbourne about a fortnight ago - here is another photo with the toes of my gym-boots so you can see the size.
At the time I didn't know what it was but suspected that it was the egg case of some sort of shark or ray. After a little wandering about the www I think that it was most probably an Elephant Shark or Callorhynchus milii. When hatched this is a funny looking thing - not quite a shark but a closely related Chimaerid - here are some links for lots - more - information.