Orthorhabdus serratus Bramlette and Wilcoxon, 1967
Elongate nannolith with three blades. Display tangential c-axis in the side view [perpendicular to the length of the blades]. The surfaces or periphery of the blades may be ornamented with ridges.
Orthorhabdus differs from Triquetrorhabdulus by having a tangential c-axis in plan view, whereas the latter has an axial c-axis.
Orthorhabdus is distinguished from Pennalithus by having three blades in different planes, whereas in the latter, two of the three blades are in the same plane. Moreover, in the plan view, Pennalithus has a vertical c-axis (c-axis parallel to the microscope's axis).
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.