Upper Jurassic Period, 155 million years BP. A Rastellum carinatum bivalve or fossil oyster. 130 grams, 81mm (3 1/4"). From an old Bristol paleontological collection; from Tulear Province, Madagascar. Rastellum Carinatum specimens have wide, angled ribs that have led to it being called the 'denture clam'; the zig-zag join between the two shells stopped coarse dirt and debris entering the shell and damaging its soft body. Like modern oysters, it lived in shallow coastal waters including the interstitial zone and fed on food particles that it filtered out of the sea water. [No Reserve]