Many persons aided this study; to whom we would especially like to extend our heartfelt appreciation. W. Counterman, Department of Paleontology at the Calvert Marine Museum, arranged the loan (through V.P. Schneider of the North Carolina Museum of Natural Sciences) of the Calvert Formation teeth. G. Fonger made his collection of Belgrade Formation specimens available to us. Without them we would never have seen the phenomena described here. I.G. Gilmore, Plant Geologist with the Potash Corporation of Saskatchewan (current owner of the Lee Creek Mine), discussed mining operations with us. V. McCollum donated the eight H. curvatus teeth used here. R. Purdy, Museum Specialist at the National Museum of Natural History (Smithsonian Institution) gave us several valuable suggestions and a lot of encouragement. V.P. Schneider, Curator of Paleontology, and P.G. Weaver, Collection Manager, Paleontology and Geology, at the North Carolina Museum of Natural Sciences, gave valuable advice in the preparation of this paper. Mr. Schneider also allowed us access to the Museum's extensive collection of fossil shark teeth. S. Snyder, Professor of Geology and Associate Dean of Arts and Sciences at East Carolina University, provided valuable information on the Pungo River and Yorktown Formations exposed in the Lee Creek Mine. K. Young and P. Young lent us the Pungo River reject specimens used here. The Editors, W. Hagadorn and P.D. Polly, the Managing Editor, J. Rumford, and two anonymous reviewers of Palaeontologia Electronica helped make this a far better paper than its first submitted version.