John W.M. Jagt, and Ger P.H. Michels. “Additional Note on the Echinoid Genus Cyclaster from the Late Maastrichtian of Northeastern Belgium”. Netherlands Journal of Geosciences (January 1, 1990): 179-185. Accessed April 3, 2026. https://njgjournal.nl/index.php/njg/article/view/12861.