These planorbids (Glyptophysa georgiana) met a sticky end in the Leeuwin-Naturaliste National Park, Western Australia. Large numbers of dead shells are concentrated in depressions along the cliff tops. Presumably they were frolicking around in ephemeral ponds, grazing on algae. Then their homes dried out. It always ends in tears.
Something made a meal of them. But what? A mouse? Mice and rats enjoy snacking on snails, as this photo of Theba pisana indicates. But as Glyptophysa is only about 18 mm long, the assailant was probably smaller than a mouse. A beetle perhaps?