Light and electron microscopic examination of centrifuge material collected off NW-Africa revealed the presence of 20 species of holococcolithophorids. Two new genera are described, Calyptrolithophora HEIMDAL with dimorphic coccoliths of the "calyptrolith" type and Laminolithus HEIMDAL with dimorphic coccoliths of the "laminolith" type. Diagnoses are presented of 3 new species, Corisphaera multipora GAARDER, Crystallolithus rigidus GAARDER, Helladosphaera poritectum HEIMDAL and of a new form, Zygosphaera divergens HALLDAL & MARKALI f. tuberosa HEIMDAL. New combinations are proposed for 7 species and specimens referable to Zygosphaera wettsteinii KAMPTNER are placed in two different genera.