1. Department of Palaeozoology, Swedish Museum of Natural History, Box 50007, S-104 05 Stockholm, Sweden;
2. Department of Cell Biology and Anatomy, Johns Hopkins University, School of Medicine, 725 North Wolfe Street, Baltimore, Maryland 21205, U.S.A.;
3. present address: New York College of Osteopathic Medicine of New York Institute of Technology, Old Westbury, Long Island, New York 11568, U.S.A.;