I. Walaszczyk, J.W.M. Jagt, and N. Keutgen. 2010. “The Youngest Maastrichtian ‘true’ Inoceramids from the Vijlen Member (Gulpen Formation) in Northeast Belgium and the Aachen Area (Germany)”. Netherlands Journal of Geosciences 89 (September):147 -67. https://doi.org/10.1017/S0016774600000755.