Triquetrorhabdulus carinatus Martini, 1965
Elongate nannolith has three birefringent blades with an axial c-axis [parallel to the length of the blades]. The width of the blade various even within the same species. The surfaces of the blades may be ornamented with ridges. The blades are making equal angles to each other.
Triquetrorhabdulus differs from Velonalithus Varol in prep. by having an axial c-axis, whilst the latter has a tangential c-axis. Moreover, the blades joined each other at a different angle in Velonalithus, whereas the blades' angles are equal in Triquetrorhabdulus.
Triquetrorhabdulus is distinguished from Triamutilaferrum in its plan view by having a biconical shape with a tangential c-axis. The latter has blades truncated at one end with a vertical c-axis.
Orthorhabdus, in its side view, is a hockey-stick shape nannolith displaying high birefringence with a tangential c-axis. In contrast, Velonalithus is a biconical form in every profile.
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.
Martini, E., (1965): Mid-Tertiary calcareous nannoplankton from Pacific deep-sea cores. - Colston Papers. 17: 393-411.