First of all, the author expresses sincere gratitude to the late Dr Murray J. Barrett who invited him to Adelaide and allowed him to study the excellent dental casts of Aborigines collected by the Department of Dental Science, the University of Adelaide. Without his generosity the data used in this study could not be available. Sincere thanks are due also to Professor A. M. Horsenell and Dr T. Brown of the University of Adelaide for their encouragement during and after the investigation in Adelaide.

The author is also grateful to Dr A. A. Dahlberg of the University of Chicago, Dr T. D. Stewart of U.S. National Museum of Natural History, Dr L. A. Altemus of Howard University in Washington, D. C., and Professor N. W. G. Macintosh of the University of Sydney, for their kind support for studying the dentition of Caucasians, Pima Indians, Eskimos, American Negroes and Queensland Aborigines.

In addition, it should be mentioned here that the investigations in Adelaide were aided by a Leverhulme Visiting Fellowship in Australia to which the author is deeply obliged. Finally the author is indebted to Miss Mariko Izuchi for her assistance in preparing the manuscript of this paper.