Abstract
A vertical stratigraphic sequence of interrelated older Senonian and Maestrichtian dinoflagellate cysts is delineated in samples from offshore well in Gabon. The lineage is a morphologically transitional evolutionary series and its earliest morphotypes, simple peridinioid cysts with three horns and globose to sub‐pentagonal outlines, are assigned to De‐flandrea laevigata sp. nov. Succeeding lineage members, related by their wall structures and archeopyles, are assigned to Svalbardella Manum 1960 and Palaeocystodinium Alberti 1960. Svalbardella polymorpha sp. nov. is defined.