Rastellum "Zig-Zag" Oyster Fossil, Madagascar

Late Cretaceous

Always a curious show-stopper, these little bivalve oysters can be found in many places over the globe. The zig-zag design between the two shells stopped coarse dirt and debris entering the shell and damaging its soft body. (Arctostrea, Lopha, Alectryonia and Ostrea are all listed as synonyms of Rastellum) Pictures are representative samples.