J. A. Clement-Westerhof, J. G. L. A. van der Eem, A. W. van Erve, J. J. Klasen, W. M. L. Schuurman, and H. Visscher. 1974. “Aspects of Permian, Triassic and Early Jurassic Palynology of Western Europe - A Research Project”. Netherlands Journal of Geosciences, January, 329-41. https://njgjournal.nl/index.php/njg/article/view/14469.