I am much indebted to many courteous paleontologists and technicians in the preparation of this manuscript: Professor Emeritus Teiichi Kobayashi (Japan Academy) for his continuous encouragement, upon whose suggestion I have been studying Mesozoic bivalves for twenty years; Professor Tetsuro Hanai (University of Tokyo) for his kind advice on the planning of this work and his reading of the final draft of this manuscript; Professor Tatsuro Matsumoto (Kyushu University) for his instructive advice on the cataloguing of the Japanese Inoceramidae and his permission to study the specimens at the Kyushu University; Dr. Mitsuo Nakano (Hiroshima University) for his kind suggestion on the classification of the Trigoniidae; Professor Minoru Tamura (Kumamoto University) for the discussion on the systematic treatment of some doubtful taxa; Professor Koichiro Ichikawa (Osaka City University), Professor Yoshihisa Ohta (Fukuoka University of Education) and Dr. Katsura Oyama (Geological Survey of Japan) for their courteous suggestions on the classification of the Bivalvia; Professor Yokichi Takayanagi (Tohoku University) for his permission to examine the type specimens at the Tohoku University; Mr. Niall Mateer (Uppsala University) for the grammatical improvement of the manuscript; Mr. Takeo Ichikawa and Mr. Norimasa Nishida for their patient assistance in the curatorial work and photography at our museum. Acknowledgments are also due to Professor Takeshi Sekino, the Director, and other staff of the University Museum, University of Tokyo, for their kind effort and arrangement in the publication of this study.