Journal of the Faculty of Science, Hokkaido University. Series 4, Geology and mineralogy;Vol.XXI, No.4


On Some Dosinia from the Pliocene and Pleistocene Formations in Hokkaido, Japan

Takagi, Toshio

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Examination of many collections of Plio-Pleistocene dosinids from Hokkaido reveals that a new distinct species, Dosinia tomikawensis, described herein, has been lumped together with D. tatunokutiensis or D. japonica. D. tomikawensis is distinguished from D. tatunokutiensis and D. japonica by an obscure escutcheon and a rather long ligament. These three species are not known to co-occur, and they may each have differrent stratigraphic and paleozoogeographic ranges. D. tomikawensis occurs in the Pliocene deposits of (1) the Horokaoshirarika Formation, Takikawa, central Hokkaido, (2) the Yuchi Formation, Teshio, northern Hokkaido, (3) the Atsuga Formation, Hidaka Monbetsu, southern part of central Hokkaido. (4) the Togawa Formation, Aomori, and (5) the Maruyama and the Nutov Formations in southern Sakhalin, and in the provincial Pleistocene deposits of (1) the Tomikawa Formation, Hakodate, southwestern Hokkaido, (2) the "upper Yuchi Formation" and the Sarabetsu Formation, Tenpoku, northern Hokkaido, and (3) the Omma Formation, Kanazawa, Ishikawa Prefecture. The occurrence of this species may suggest that this species retreated south- and westward from the adjacent waters of Sakhalin to the present northern-most limits within the warm Tsushima Current with the water temperature deterioration during the lapse of Pliocene to Pleistocene.