Abstract
The writer studied borings made by some kind of Polydora in the shells of Babylonia japonica (Reeve) collected from the Pleistocene formation, Crassostrea gigas (Thunberg) and Mactra (M.) chinensis Philippi from the inner site of Tokyo Bay.
In this short paper, he described the morphological characters of them with special remarks on the difference of above three specimens. After the penetration, it makes very thin shell layer secondarily. Especially in case of Mactra and Crassostrea, they make a dome respectively inside of the shell. He made some considerations about the boring behavior of Polydora in the shell layer.
