Harold Voris researched and directed this project and the preparation of the maps. Clara Simpson, a scientific illustrator at The Field Museum, drew the maps presented here. Clara Simpson's skill in map interpretation and computer graphics proved invaluable and her patience with the innumerable modifications and refinements required is greatly appreciated. Thanks go to Julian Dodson, Jack Fooden, Larry Heaney, Robert Inger, Daryl Karns, John Murphy and Helen Voris for helpful comments and suggestions on the manuscript and the maps. Thanks also go to Chris Winters at the University of Chicago Map Library for his kind assistance and special thanks are due Ingrid Fauci for her technical assistance.