Gebhardt Holger, Cenomanian to Coniacian ostracodes from the Nkalagu area (SE Nigeria): biostratigraphy and palaeoecology, Palaontologische Zeitschrift Palaontologische Zeitschrift (Print);Journal of Palaontologische Gesellschaft Scientific contributions to palaeontology, 73(1/2), 1999, pp. 77-98