John W.M. Jagt, and W. James Kennedy. “Acanthoscaphites Varians (Lopuski, 1911) (Ammonoidea) from the Upper Maastrichtian of Haccourt, NE Belgium”. Netherlands Journal of Geosciences, Jan. 1989, pp. 237-40, https://njgjournal.nl/index.php/njg/article/view/12899.