1. Department of Paleontology, Calvert Marine Museum, P.O. Box 97, Solomons, MD 20688, U.S.A.,
2. Research Associate, Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC, 20013-7012, U.S.A.
3. 3403 Willow St., Chesapeake Beach, MD 20732 Maryland, U.S.A.,
4. Department of Vertebrate Paleontology, American Museum of Natural History, 200 Central Park West, New York, NY 10024, U.S.A.