Article: Preserved ligaments in Australian Permian bivalves

The Australian Permian 'burrowing' bivalves have large external ligaments which may be either replaced by calcite or have their outer surfaces preserved as external and internal moulds. Sections of two such replaced ligaments of Pyramus laevis and Megadesmus nobilissimus show three layers which probably correspond to the inner, outer, and fusion layers of living bivalves. The presence effusion layer is to be expected from the lack of pallial attachment above the adductor muscles, and its presence in Megadesmus and Pyramus may prove to be useful in differentiating these shells from more or less homeomorphic living (and fossil) shells which have no fusion layer.