The Toko Bay is one of the larger indentations along the Pacific coast of Honshu. The remains of molluscan shells collected from 21 stations in this bay (see fig. 1), consisted of 119 species, viz. 60 pelecypods, 56 pastropods and 3 scaphopods. The dominant species among them were the following 5 species, namely, Theora lubrica Gould, Raeta yokohamensis Pilsbry, Aluenius ojianus (Yokoyama), “Gingula” matusimana Nomura and Siphonodentalium n. sp.. While the unmber of species collected from single station was larger on sandy bottoms of Nakanose and Futtsu areas, the unmber of speciemens was larger on muddy bottoms of north-east area and decreased toward the south-wast area. The distribution of Theora lubrica and Raeta yokohamensis, which are indicator animals of strong embayment, was thicker in the north-east area than in the south-west. Aluenius ojianus was more unmerous in the south-east area. These thanatological results seem to indicate that the cline of ecological conditions in from the weak embayment character of the south-west to the stronger of the north-east. Among notable species there were Pyrunculus tokyoensis Habe, an endemic species to this bay and Lucinoma annulata (Reeve) which are may be a northern relic. Cylichnatys striata (Yamakawa) and Eufenella pupoides (A.Adams) which are common constituents of the benthos of bays on the southern Pacific coast of Honshu, were not found in this bay. The molluscan remains near the mouth of this bay had the affinity not to the funa of mouths of bays in southern Japan, but to that of continental shelf bordering Japan, its characteristic species being Sarepta Speciosa (A. Adams), Enida japonica (A. Adams) and Limopsis tajimae Sowerby.
