A.A. Klompmaker, and B.J.H.M. van den Berkmortel. “Earliest Jurassic (Hettangian) Psiloceratoid Ammonites from a Subrosion Pipe at Winterswijk, the Eastern Netherlands”. Netherlands Journal of Geosciences, vol. 86, Dec. 2007, pp. 379 -88, doi:10.1017/S0016774600023593.