Samuel Fessenden Clarke was the leading specialist on hydroids (phylum Cnidaria) in North America over the last quarter of the nineteenth century. During that period he published taxonomic papers on hydroids from both the Atlantic and Pacific coasts of the continent, from the Gulf of Mexico, and from the eastern Pacific off Central and South America. He also authored a section on hydrozoan biology for “The Riverside Natural History” series. Most of his papers on hydroids were published while he was in his twenties. Clarke described as new 61 nominal species, three nominal genera, and one nominal family, as well as two “varieties” of hydroids. A list of these, and their current taxonomic status, appears in the present work. Clarke consistently provided sound descriptions and locality data for all supposed new species, and drew accurate illustrations of most of them. His research on Hydrozoa, beyond alphataxonomy, was directed towards faunal distributions and the use of hydroid assemblages as biogeographic indicators. In addition to investigations on hydroids, Clarke carried out research on the developmental biology of amphibians and reptiles. His doctoral dissertation at Johns Hopkins University was based on the embryology of the “Spotted Salamander” (=Yellow-spotted Salamander), and he published a major paper on the habits and embryology of the American Alligator. Most of Clarke's career was devoted to academic duties at Williams College, Massachusetts, where he was recognized as a dedicated and inspiring teacher. He served the American Society of Naturalists in various capacities, including a term as its president, was an influential trustee of the Marine Biological Laboratory, Woods Hole, and promoted the study of science in American schools.
