In the western part of Joetsu City, the Pliocene strata are subdivided into the Kawazume, Nadachi and Tanihama formations in upward sequence. The following four molluscan associations occur in the Nadachi Formation; Acila-Portlandia (lower sublittoral zone), Nuculana (lower sublittoral to bathyal zone), Delectopecten (bathyal zone) and Calyptogena (bathyal zone) associations. The first association also occurs in the Tanihama Formation and the last is recognized in the Kawazume Formation. These associations include rich protobranch bivalves more than those in shallower waters. The lower sublittoral association shows a higher species diversity than the bathyal one.
Sixteen fossil Balanomorpha and one fossil Lepadomorpha were found from Pleistocene coastal terrace deposits at two localities in the southwestern part of Kochi Prefecture, Shikoku. Many of them indicate first fossil records in Japan and the southernmost occurrences in the Pleistocene. The species from the Hirano Formation (Loc. 1) are mainly composed of inhabitants in the upper sublittoral and intertidal zones of an open sea. Most species from the Ashizuri Formation (Loc. 2) are inhabitants in similar zones of an embayment.