Carbonic age from the American continent had been made in 1868 by Meek and Worthen who described Eurypterus mazonensis from the Coal Measures of Illinois, erecting for it the subgenus Anthraconectes, and in 1877 C. E. Hall described two species (E. pennsylvanicus and E. mansfieldi) from the Coal Measures of Pennsylvania. James Hall noted four species from the Carbonic of that State, adding two types to those before known, and he described besides a new form from the Chemung group of Warren, Pa. (E. beecheri) which Beecher later determined to be a Stylonurus.
Considerable progress in the understanding of the organization of the eurypterids and especially of the genera Eurypterus and Pterygotus, was made by Fr. Schmidt's admirable investigations entitled Die Crustaceenfauna der Eurypterenschichten von Rootziküll auf Oesel published in 1883. Nieszkowski's work had already been done under Dr Schmidt's supervision and Schmidt now carried out a very detailed examination of the remains of Eurypterus fischeri and Pterygotus osiliensis. He was thereby enabled to correct many details of Hall's and Nieszkowski's descriptions of the appendages; to show the existence of five "Blattfüsse" or sternites open on the ventral side, as in Limulus; to recognize sexual differences in the opercular appendages; to establish the correct number of walking legs in Pterygotus (8, while Woodward assumed 6), and the form and position of the epistoma.
In 1884 Whiteaves made known an Eurypterus (E. boylei) from the Guelph limestone of Canada, and in 1888 Matthew described as Eurypterella ornata, a peculiar Devonic organism that is referred by him to this group.
In this year, 1888, also appeared volume 7 of the Palaeontology of New York by Hall and Clarke. This volume supplements the description of the Siluric eurypterids in volume 3, by bringing together the remaining merostomes from the State of New York and the adjoining regions. It contains a full size drawing of Hall's type of the famous carapace of Stylonurus excelsior and gives an
