Three-dimensionally preserved Richmondian Graptolites from southwestern Ohio and the Graptolites Correlation of the north American Upper Ordovician Standard
E. Mitchell C et M. Bergstrom S, Three-dimensionally preserved Richmondian Graptolites from southwestern Ohio and the Graptolites Correlation of the north American Upper Ordovician Standard, Bollettino della Societa paleontologica italiana , 16(02), 1977, pp. 257-270