Willems, 1995b

Willems, H., 1995b: Praecalcigonellum duopylum n. sp., a new calcareous dinoflagellate cyst from the lowermost Danian (Biantholithus sparsus Zone) of the Geulhemmerberg Section (South Limburg, The Netherlands). Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, v.198, p.141-152, pl.1-3.