抄録
Molluscan fauna of the "Miocene" Maejima Formation is examined from taxonomical, biostratigraphical and paleozoogeographical points of view. It is composed of four gastropods and 14 bivalves including a new species. Two assemblages, the Isognomon and the Megangulus-Acila assemblage, were discriminated. The Isognomon assemblage is autochthonous or para-autochthonous and is composed of elements inhabited the littoral to upper sublittoral gravelly to rocky bottom in a warm sea. The Megangulus-Acila assemblage represents a mixed composition between muddy sand and gravelly to rocky bottom elements, and was formed in an upper sublittoral muddy bottom near a rocky shore. Occurrences of Megangulus maximus (Nagao), Isognomon (Hippochaeta) hataii Noda and Furuichi and Chlamys (Leochlamys) namigataensis (Ozaki) indicate the age of the Maejima Formation as the Paleogene, not the Miocene. The molluscan fauna of the Paleogene Maejima Formation contains both Tethyan Indo-Pacific elements and Northern Pacific elements. Taxonomy of selected molluscan taxa including a new arcid, Arca (Arca) uedai sp. nov., is described or discussed.
