Flower, R.H. 1976; Ordovician Cephalopod Faunas and Their Role in Correlation, s. 538-541; proceedings pub. Paleontological Association, Gr Br. Hook, J.C. and Flower, R.H. 1976; and the Origin of the Troedsonnellidae. Jour Paleontology vol 50, no 2, s. 293-300, mar. 1976 Sweet, W.C, 1964; , s. 225-226 i Orthoceratidae, s. 224-231 i Vol K. GSA and Univ Kansas Press.