Helenea staurolithina Worsley, 1971
Microstaurus Black, 1971a
Circular to elliptical placoliths are constructed of a cretarhabdid pelaga sloping towards the central area and formed of inclined segments that are typically weakly clockwise-imbricated, but occasionally non-imbricate, and a central area characterised by an axial cross supporting a short, solid distal process with a distinct square-shaped termination. The axial cross may be slightly rotated relative to the long axis of the placolith. The arms of the cross have blunt, pointed or bifurcated terminations. There are no lateral bars in the central area.
The entire placolith exhibits first-order, greyish-white interference colours. The The placolith generally displays first-order, greyish-white interference colours; however, it becomes dimmer towards the periphery, where only the inner layer of the distal shield is developed. In plan view under crossed polars, the outer layer of the distal shield exhibits inclined extinction and length-fast (–) elongation.
Black, M. 1971a. Coccoliths of the Speeton Clay and Sutterby Marl. Proceedings of the Yorkshire Geological Society 38: 381-424.
Worsley, T. R., 1971. Calcareous nannofossil zonation of Upper Jurassic and Lower Cretaceous sediments from the Western Atlantic. In: Farinacci, A. (ed.), Proceedings of the Second Planktonic Conference Roma 1970. Edizioni Tecnoscienza, Rome vol. 2, pp. 1301-1321.