Énay, Raymond, and Michael K. Howarth. “Stevensites, Zittelites, and Gyrophylloceras, New Generic Names Proposed for Stevensia Énay, 2009, Zittelia Tavera Benitez, 1985, and Gyrophyllites Wiedmann, 1963 (Mollusca: Ammonoidea)”. Paleontological Contributions, no. 19, Apr. 2018, pp. 1-2, https://doi.org/10.17161/1808.26312.