抄録
Twenty-five molluscan taxa were identified from three localities of the lower Middle Miocene Arakawa Formation in the Iwadono Hills area, Saitama Prefecture, central Japan. This fauna consists of two types of assemblage (protobranch-dominant and septibranch-dominant) and is inferred to represent a deep-water fauna (bathyal depths) on the basis of its taxonomic structure. Similarities in generic composition between the molluscan fauna of the Arakawa Formation and that of the bathyal zone in modern Sagami Bay suggest that the marine climate during the Arakawa deposition is comparable with that of the intermediate water of Sagami Bay. One new species, Neilonella tsukigawaensis, is described herein, and the stratigraphic relationship between the Arakawa and the overlying Goudo Formation is briefly mentioned.
