Sphenolithus intercalaris Martini, 1976
Species of Furcatolithus Martini (1965) have a cone shape duolithic apical spine. The proximal cycle is vestigial. In cross-polarised light, the apical spine with axial c-axis shows maximum birefringence at 45° but extinct (dim) at 0° [the axial suture between the two helves is better seen at this orientation].
Furcatolithus intercalaris differs from Furcatolithus celsus (Haq, 1971) Howe, 2021 by the lack of proximal cycle.
Haq, B. U., 1971. Paleogene calcareous nannoflora. Parts I-IV. Stockholm Contributions in Geology 25, 1-158.
Howe, R., 2021. Ultrastructure and taxonomy of the family Sphenolithaceae. Journal of Nannoplankton Research 39(1), 29-75.
Martini, E., 1976. Cretaceous to Recent calcareous nannoplankton from the Central Pacific Ocean (DSDP Leg 33). Initial Reports of the Deep Sea Drilling Project 33, 383-423.
DSDP Leg 33, Site 317B, Central Pacific Ocean