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.