Calcidiscus quadriperforatus Kamptner, 1950
Cyclococcolithus Kamptner, 1954
Tiarolithus Kamptner 1958
Cyclococcolithina Wilcoxon, 1970
Striatococcolithus Bukry, 1971
Circular to elliptical placoliths have two monocyclic shields and a closed or narrowly open central area. The non-birefringent distal shield is greater than the birefringent proximal shield.
Calcidiscus differs from Umbilicosphaera Lohmann (1902) and Pedinocyclus Bukry & Bramlette (1971) [subtitute for Leptodiscus Bukry & Bramlette, 1969] by having a distal shield larger than the proximal shield. Umbilicosphaera has a proximal shield greater than the distal shield, whereas Pedinocyclus has equal diameter shields. The proximal shield of the Calcidiscus is birefringent, whereas Cryptococcolithus Gartner (1992), Umbilicosphaera and Pedinocyclus have non-birefringent shields.
Species of the Calcidiscus are differentiated based on their shape [elliptical or circular], presence or absence of central opening, central structure and overall size.
Bukry, D., (1971): Cenozoic calcareous nannofossils from the Pacific Ocean. - San Diego Society of Natural History Transactions. 16: 303-327.
Bukry, D. & Bramlette, M. N., (1969): Some new and stratigraphically useful calcareous nannofossils of the Cenozoic. - Tulane Studies in Geology. 7: 131-142.
Bukry, D. & Bramlette, M. N., (1971): Validation of Pedinocyclus and Quinquerhabdus new calcareous nannoplankton genera. - Tulane Studies in Geology and Paleontology. 8: 122-122.
Gartner, S., (1992): Miocene nannofossil chronology in the North Atlantic, DSDP Site 608. - Marine Micropaleontology. 18: 307-331.
Kamptner, E., (1950): Über den submikroskopischen Aufbau der Coccolithen. - Anzeiger der Österreichische Akademie der Wissenschaften, Mathematische-Naturwissenschafliche Klasse, Wien. 87: 152-158.
Kamptner, E., (1954): Untersuchungen über den Feinbau der Coccolithen. - Archiv für Protistenkunde. 100: 1-90.
Kamptner, E., (1958): Betrachtungen zur Systematik der Kalkflagellaten, nebst Versuch einer neuen Gruppierung der Chrysomonadales. - Archiv für Protistenkunde. 103: 54-116.
Lohmann, H., (1902): Die Coccolithophoridae, eine Monographie der Coccolithen bildenden Flagellaten, zugleich ein Beitrag zur Kenntnis des Mittelmeerauftriebs. - Archiv für Protistenkunde. 1: 89-165.
Wilcoxon, J. A., (1970): Cyclococcolithina Wilcoxon nom. nov. (nom. subst. pro Cyclococcolithus Kamptner, 1954). - Tulane Studies in Geology and Paleontology. 8: 82-83.