Orthorhabdus serratus Bramlette and Wilcoxon, 1967
Emended Diagnosis: An elongated nannofossil with three blades, truncated at one end and pointed at the other. The species of Orthorhabdus can naturally settle in the plan view and appear in constant extinction (the optic axis is vertical relative to the microscope stage in this orientation). Orthorhabdus can also naturally settle in the side view, appears hockey stick-like, and displays strong birefringence in first-order white to yellow colours. Orthorhabdus exhibits inclined extinction (extinction angle
is about 20°) and length-fast (-) elongation in this 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.
Varol, O. 2025a. A practical guide to optical studies of calcareous nannofossils. Grzybowski Foundation Special Publication. 29: 1-222