Triquetrorhabdulus rugosus Bramlette & Wilcoxon, 1967
Orthorhabdus rugosus (Bramlette & Wilcoxon, 1967) Young & Bown 2014
Broad species of Pennalithus have three unequal size blades. The c-axis is vertical [vertical to the natural settling of the form/ parallel to the microscope's optical axis]. The blades are pointed at both ends, but more pointed at one end than the other end. The dentate blade is the widest and ornamented by transverse striations. The median blade is straight.
Pennalithus rugosus differs from Pennalithus farnsworthii (Gartner, 1967) by having a straight median blade, whilst the latter has a distinctly curved median blade.
Pennalithus rugosus is distinguished from Pennalithus striatus (Müller, 1974) by lacking additional longitudinal ridges.
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.
Gartner, S., (1967): Calcareous nannofossils from Neogene of Trinidad, Jamaica, and Gulf of Mexico. - University of Kansas Paleontological Contributions, Papers. 29: 1-7.
Müller, C., (1974): Calcareous nannoplankton, Leg 25 (Western Indian Ocean). - Initial Reports of the Deep Sea Drilling Project. 25: 579-633.
Theodoridis, S., (1984): Calcareous nannofossil biostratigraphy of the Miocene and revision of the helicoliths and discoasters. - Utrecht Micropaleontological Bulletin. 32: 1-271.
Young, J. R. & Bown, P. R., (2014): Some amendments to calcareous nannoplankton taxonomy. - Journal of Nannoplankton Research. 33(1): 39-46.
Cipero Section, Trinidad