A new calcareous dinoflagellate cyst species, Tetratropis terrina sp. nov., with an apparent stratigraphically narrow range is described from the Upper Campanian Bostrychoceras polyplocum zone of the Lägerdorf chalk sequence (NW Germany). The electron microscopic and light microscopic analyses show that T. terrina has both a pithonelloid wall type with uniformly inclined wall crystallites and a reduced peridiniacean paratabulation pattern. The prominent morphological similarities of T. terrina to the other two Tetratropis species (T. patina and T. corbula) justify the affiliation of the new species to the genus. As a result of the extension of the morphological spectrum by the new species, the genus Tetratropis Willems, 1990 has been emended.