Tetralithus obscurus Deflandre, 1959
Phanulithus Wind & Wise in Wise & Wind 1977
Elliptical, rarely subcircular holococcoliths with a narrow outer wall, usually four but rarely five crystalline blocks, and a distal process supported by variable numbers of struts producing depressions between adjacent struts.
In plan view under crossed polars, the outer wall and the crystalline blocks of this holococcolith display interference colours and exhibit parallel extinction (extinction angle 0°) and length-slow (+) elongation in their natural position.
Calculites has often been used as a taxonomic dustbin for holococcoliths that display highly variable constructional morphologies and optical properties. In this study, forms characterised by four crystalline blocks exhibiting whitish-grey interference colours and lacking a distal process are assigned to Asapholithos. Varol (2025a) has already reassigned Calculites maghredaswampensis to Swapansahooia maghredaswampensis on the basis of the structural and optical properties of its distal process. Further work is in progress on holococcolith species not treated in the present study but commonly assigned to Calculites (e.g. Calculites cenomanicus and Calculites percernis).
Deflandre, G. 1959. Sur les nannofossiles calcaires et leur systématique. Revue de Micropaléontologie 2: 127-152.
Sissingh, W. 1977. Biostratigraphy of Cretaceous calcareous nannoplankton. Geologie en Mijnbouw. 65(1): 37-65.
Wise, S. W. & Wind, F. H. 1977. Mesozoic and Cenozoic calcareous nannofossils recovered by DSDP Leg 36 drilling on the Falkland Plateau, south-west Atlantic sector of the Southern Ocean. Initial Reports of the Deep Sea Drilling Project. 36: 269-491.