Sphenolithus predistentus Bramlette & Wilcoxon, 1967
Sphenolithus tribulosus Roth, 1970
Furcatolith has a shallow hollow conical frustum shape proximal cycle and a long apical spine broadening at the proximal end. The cone shape duolithic apical cycle has a flat base. The height of the apical spine varies greatly and may have various length bifurcation distally.
In cross-polarised light, the apical spine with axial c-axis displays maximum birefringence at 45° but extinct (dim) at 0° [the axial suture between the two helves is better seen at this orientation].
The shallow, empty frustum shape proximal cycle has a much narrower diameter than the diameter of the apical spine at its base.
Furcatolithus predistentus differs from all other species of Furcatolithus Martini, 1965 by a distinct broadening of the apical spine at its base. It is further distinguished from all other Furcatolithus species by having a proximal cycle with a much narrower diameter than the diameter of the apical spine at its base.
Bramlette, M. N., Wilcoxon, J. A., 1967. Middle Tertiary calcareous nannoplankton of the Cipero section, Trinidad, W.I. Tulane Studies in Geology and Paleontology 5, 93-131.
Howe, R., 2021. Ultrastructure and taxonomy of the family Sphenolithaceae. Journal of Nannoplankton Research 39(1), 29-75.
Martini, E., 1965. Mid-Tertiary calcareous nannoplankton from Pacific deep-sea cores. Colston Papers 17, 393-411.
Roth, P. H., 1970. Oligocene calcareous nannoplankton biostratigraphy. Eclogae Geologicae Helvetiae 63, 799-881.
Bramlette & Wilcoxon, 1967
Cipero Section, Trinidad