Reference
Cyprian Kulicki, Neil H. Landman, Michael J. Heaney, Royal H. Mapes, Kazushige Tanabe (2002): Morphology of the Early Whorls of Goniatites from the Carboniferous Buckhorn Asphalt (Oklahoma) with Aragonitic Preservation – Abhandlungen der Geologischen Bundesanstalt in Wien – 57: 205 - 224.