Allan Larson1, David B Wake2, Linda R Maxson3, Richard Highton4. 1. Department of Genetics and Museum of Vertebrate Zoology, University of California, Berkeley, California, 94720. 2. Museum of Vertebrate Zoology and Department of Zoology, University of California, Berkeley, California, 94720. 3. Departments of Genetics and Development, and of Ecology, Ethology,and Evolution, University of Illinois, Urbana, Illinois, 61801. 4. Department of Zoology, University of Maryland, College Park, Maryland, 20742.