Acknowledgements
Ellis Yochelson, of the U. S. Geological Survey, Washington, D. C., helped launch this study and offered helpful comments on the morphology of aptychi. His review of a previous version of this manuscript was quite helpful. While our conclusions differ in some particulars, his comments were most constructive. Roy Mapes, Ohio University, also helped to considerably improve the manuscript. The Palaeontological Institute of the University of Lund loaned the Aptychopsis specimens for comparison. Jann Thompson of the U. S. National Museum located one of Clarke's holotypes and those from Cooper's Oklahoma work, and was of much assistance in our examination of them. Mary Baum and Wendy Weitzner, of The Cleveland Museum of Natural History, helped uncover the more obscure references, and Shya Chittaley and JoAnn Coburn, CMNH, searched their collections for a few stray aptychi. Joe Hannibal, CMNH, offered tireless assistance and made possible the loan of the specimens studied. Thanks are due Richard E. Carroll of Michigan State University for collecting one of the specimens in situ and donating it to the the Cleveland Museum of Natural History for our study. Donald F. Palmer and Alan H. Coogan read an earlier draft of the manuscript.
This is Contribution 455, Department of Geology, Kent State University, Kent, Ohio 44242.