Tonromeinia bilenii

Tonromeinia bilenii Bowman & Varol, 2021

A medium-sized (5.0–8.0ìm) circular species of Tonromeinia possessing equal diameter/height two discs and a low column with a featureless central area lacking a tube cycle.

After Bilen Varol, London, United Kingdom.

Overall height: 2.37μm; Overall diameter (max): 5.49μm; Central Opening diameter: 2.68μm.

Medium size (5.0–8.0μm) circular, rarely subcircular species having two discs, a column and a futureless central area without a tube cycle. The discs and the low column display similar height/thickness and equal diameter, and the species appears compressed in side-view. Tonromeinia bilenii is consistently observed only in plan-view because the limited height of the column prevents sufficient mass distribution along the height axis.

In cross-polarised light, the dextrogyre extinction lines appear on the distal side, whereas the laevogyre extinction lines signify the proximal side. Regarding the profile using a gypsum plate, the coordination of the horizontal axis and the blue region represents the distal side, and the affiliation of the vertical axis with the blue area distinguishes the proximal side. The discs/a column are birefringent in side-view and plan-view. The discs/column generate whiteish birefringence colours in plan-view and yellowish birefringence colours in side-view.

All species of Tonromeinia that are 5.0–8.0μm in diameter are assigned to Tonromeinia bilenii, regardless of the dimensions of the central opening.

Bowman, A. R. & Varol, O. 2021. A Taxonomic Revision of Heliolithaceae - Applications in Resolving the Problematic Calcareous Nannofossil Biostratigraphy of the Paleocene. In: M. Montenary, M. (Ed.). Calcareous nannofossil biostratigraphy of the Stratigraphy and timescales. 6: 43-223.