Type Species

Orthorhabdus serratus Bramlette and Wilcoxon, 1967


An elongated nannofossil with two blades, a ridge truncated at one end and pointed at the other with a toot-like projection. The species of Orhorhabdus can naturally settle in plan view and appear extinct (the c-axis is parallel to the microscope axis). Due to the development of tooth-like projection, very difficult to rotate it on its side view. Orthorhabdus is a triangular shape at its side view , having a tangential c-axis (perpendicular to the length of the specimen) with parallel extinction.


Orthorhabdus differs from Triamutilaferrum by having a tooth-like projection and parallel extinction at its side view, whereas the latter lacks a toot-like projection and has oblique inclined extinction. In both genera, two blades and the ridge are truncated at one end and pointed at the other. They have tangential c-axises at their side views and are extinct in their plan view (c-axises are parallel to the microscope axis).

The biconical Triquetrorhabdulus is distinguished from the above genera by having an axial c-axis with parallel extinction.


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.