Megascopic gastropods (2,500 specimens, 42 species, 37 genera and subgenera) are described from five of the seven known marine or brackish members of the Allegheny Series (Middle Pennsylvanian) of eastern Ohio. The Vanport limestone and shale member yielded 1,684 specimens, 35 species, and 35 genera and subgenera; the Columbiana, Washingtonville, Putnam Hill, and Dorr Run members yielded, respectively, lesser numbers. Four new species are assigned to Euphemites, Bellerophon, and Abylea, a new genus. Use of Pennsylvanian gastropods for correlation is limited until they are much better known. There is some evidence for an Allegheny-Des Moines correlation.