Colombo, M. R.; Cita, M. B. (1980): Changes in size and test porosity of Orbulina universa d'Orbigny in the Pleistocene record of Cape Bojador (DSDP Site 397, eastern North Atlantic). Elsevier, Amsterdam, Netherlands, Marine Micropaleontology, 5 (1), 13-29, georefid:1981-002563