Size 9cm x 6cm
The internal cast of a large cockle shell from a sea cliff occurance south of port lincoln. Although I have never been there , from speaking to people who have , it was a very small zone in a cliff face and only accessable at low tide. It was quite a  popular collecting locality for locals years ago. Apparentely the rock was really hard digging, resulting in a lot of broken shells. Recent information is that the deposit is completely worked out and near on impossible to find any fossils at all. The fossils are all internal casts of shells with no or little shell on the outside remaining. I have only ever seen these locally.