Pholadomya japonica was first described by M.Yokoyama in 1920, based upon two specimens from Naganuma in Toyoda-Mura not far south of Yokohama, Kanagawa-Ken.

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During the summer and early autumn of 1947, Professor S. Hanzawa and his collaborators undertook geological studies of the Tertiary and Quaternary formations of the Shimokita Peninsula, Shimokita-Gun, Aomori-Ken, and as a result, numerous fossils were collected from the different formations. Of the fossils, those belonging to the genus Turritella are treated in this article, and all are from the Hamada formation, the youngest marine fossil-bearing formation of the Tertiary sediments thereon developed.

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