The Microscopic Structures of Marginal Area of Inner Layer in Eutaxodont Shell

Abstract

Microscopic structures of the marginal area of inner layer of the shells of five eutaxodont species, Barbatia obtusoides, Scapharca subcrenata, Limopsis tajimae, Tucetona auriflua and Glycymeris yessoensis were observed. The common characters among them can be summarized as follows : 1. Inner layer is distributed only inside of pallial line. 2. Fine radial striations develop on inner layer. 3. Tubules are distributed regularly near pallial line but irregularly at the apical side. 4. Zone with tubules and zone without tubules alternate near pallial line. 5. When marginal area of inner layer shows an indentation, tubules exist on the part projected to ventral side but not on the part which enters at the apical side.