Dr. James D. Williams is an aquatic biologist at the Florida Fish and Wildlife Conservation Commission and research associate at the Florida Museum of Natural History, Gainesville, Florida. Robert S. Butler is a fish and wildlife biologist at the US Fish and Wildlife Service, Asheville, North Carolina. Gary L. Warren is a freshwater invertebrate ecologist at the Florida Fish and Wildlife Conservation Commission, Gainesville, Florida. Nathan A. Johnson is a research biologist at the US Geological Survey, Gainesville, Florida.