ACKNOWLEDGMENTS

We thank R. Beavers for his help, W. Turnbull for loan of specimens and SEM photos, J. Robbins for CT rendering, and R.A. Ketcham at the University of Texas CT lab for the scans. C.A. Repenning was an inspiration to us all. Supported by the Donors of the Petroleum Research Fund of the American Chemical Society (to L. L. J.), the Institute for the Study of Earth and Man, The Saurus Institute, and the NSF EAR 9206691 (to D.A.W.).