Clarification of an index nannofossil species for the Paleocene/Eocene boundary

There has been some confusion regarding the index nanofossil specie Discoaster diastypus, despite its frequent use in biostratigraphy. In light of this factor, the species concept should be clarified to make it more precise for use in biostratigraphy. In this regard, the sample used to describe the species in 1961 is reexamined. Its size is measured, its rays are counted and it is photographed in both plan and side views.