Abstract: The ostracods from 70 stations in the Hamana-ko region, on the Pacific Coast of central Japan, comprise 70 species belonging to 45 genera, among them, 44 species belonging to 31 genera are extant. The ostracod distribution in Hamana-ko Bay is dependent on characteristics of the water, the nature of substrate, and the bottom topography of the bay. Based on the characteristic species, 6 major biofacies and 7 sub-biofacies are recognized as follows: (I) fresh water pond and river biofacies; (II) brackish water inlet biofacies; (III) bay coast and sand bank biofacies; (IV) inner bay biofacies (dy sub-biofacies, sandy bottom sub-biofacies, silty bottom sub-biofacies, silty sand bottom sub-biofacies); (V) channel and extension channel biofacies (main channel sub-biofacies, extension channel sub-biofacies); (VI) bay mouth and open sea biofacies (bay mouth sub-biofacies, open coast sub-biofacies, onshore sub-biofacies). The standing crop size of ostracods are examined quantitatively in 27 localities. The species diversity and ratio of living specimens to the total number of specimens collected are calculated. A new genus, Neopellucistoma (type-species, Neopellucistoma inflatum n. sp.) and new species, Pontocythere sekiguchii, Pontocythere minuta, Neocytherideis punctata, Cornucoquimba rugosa, Bythocythere maisakensis, Bythoceratina elongata, Semicytherura elongata, Phlyctocythere hamanensis and Neopellucistoma inflatum are described.