The author has benefited from frequent conversations with, and the sound advice of, Prof. Barrie Jamieson (Zoology Dept., The University of Queensland, Australia), Dr. Cliff Cunningham (Zoology Dept., Duke University, USA) and Dr. Rafael Lemaitre (Dept. of Invertebrate Zoology, NMNH, USA). The author also wishes to thank the helpful staff of the Zoology Department, The University of Queensland, Australia where this project had its beginnings and the Department of Invertebrate Zoology, National Museum of Natural History, Smithsonian Institution, Washington D.C., USA, where it was completed. This paper was improved by the suggestions and comments of an anonymous reviewer. During the writing of this paper the author was funded from a Smithsonian Institution Postdoctoral Fellowship (1995-96) and an Australian Research Council Postdoctoral Research Fellowship (1996).