I thank Professor Kazushige Tanabe (Geological Institute, University of Tokyo) for providing knowledge on higher-level molluscan phytogeny, critical reading of the manuscript, and supervision throughout this study. I gratefully acknowledge Dr. Paula M. Mikkelsen (American Museum of Natural History) for constructive advice on technical, stylistic, and methodological problems and for improvement of the English in the final manuscript. I am also grateful to Dr. Tatsuo Oji (Geological Institute), Dr. Rei Ueshima (Department of Biological Sciences, University of Tokyo), and Dr. Kazuyoshi Endo (Geological Institute) for helpful discussions on characters and cladistic analysis; to Dr. Tomoki Kase (Department of Geology, National Science Museum) and Dr. Ryuichi Majima (Yokohama National University) for valuable comments on implications of shell characters; and to Professor Takashi Okutani (College of Bioresource Sciences, Nihon University) for many practical suggestions on archaeogastropod systematics and associated references. Thanks are also due to Professor Susumu Segawa (Tokyo University of Fisheries) for providing laboratory space and facilities for anatomical work.

With regard to material, I especially thank Mr. Eiji Tsuchida (Ocean Research Institute, University of Tokyo) for rare species of deep-sea taxa dredged or trawled by R/V Tansei-Maru, and Mr. Hiroshi Ishikawa (Ehime Prefectural Yoshida High School) for many carefully preserved specimens of shallow-water species. The greater part of this material was also made available through the courtesy of the following persons: Mr. Yasufumi Arima (Amami-Oshima); Dr. Katsunori Fujikura (Japan Marine Science and Technology Center); Dr. Kazunori Hasegawa (Showa Memorial Institute, National Science Museum); Mr. Kazumasa Hashimoto (Ishigaki Tropical Station, Seikai National Fisheries Research Institute); Dr. Shigeo Hori (Tokyo University of Fisheries, TUF); Mrs. Seiko Koizumi (Tokyo); Mr. Masahiro Kono (Nansei National Fisheries Research Institute); Mr. Yasuhiro Kuwahara (Hokkaido Abashiri Fisheries Experimental Station); Dr. Hiroshi Saito (Department of Zoology, National Science Museum); Mr. Yasuo Tabakotani (Yokohama); Dr. Koichi Takenouchi (Nara); Dr. Kotaro Tsuchiya (TUF); Mr. Tomio Watanabe (Choshi, Chiba); Mr. Kensuke Yanagi (TUF). Dr. H. Saito and Dr. K. Tsuchiya kindly provided juvenile shells of Mikadotrochus beyrichii (Pleurotomariidae) that were already prepared for their own observations. This study was financially supported by a grant from the Research Institute of Marine Invertebrates.