In 1912, John Mason Clarke and Rudolf Ruedemann published "The Eurypterida of New York" in which all eurypterid species thus far recovered from fossil deposits there were discussed. Clarke and Ruedemann created one of the first phylogenetic trees of eurypterids, dividing the order into two families; Eurypteridae (distinguished by smooth eyes and including "Eurypterus", "Anthraconectes", "Stylonurus", "Eusarcus", "Dolichopterus", "Onychopterus" and "Drepanopterus") and Pterygotidae (distinguished by faceted eyes and including "Pterygotus", "Erettopterus", "Slimonia" and "Hughmilleria"). Both families were considered to be descended from a common ancestor, "Strabops". In line with earlier authors, Clarke and Ruedemann also supported a close relationship between the eurypterids and the horseshoe crabs (united under the class Merostomata) but also discussed alternative hypotheses such as a closer relation to arachnids.