Speetonia colligata Black, 1971
The placolith generally displays first-order, greyish-white interference colours, becoming 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, while the transverse bar displays length-slow (+) elongation in distal view.
The placolith comprises a cretarhabdid pelaga sloping towards the central area, formed of inclined segments that are commonly weakly clockwise-imbricated, and only rarely non-imbricate, and a distally arched central area characterised by a transverse bar that supports a short distal process. The central area lacks additional structure on either side of the transverse bar.
Black, M. 1971a. Coccoliths of the Speeton Clay and Sutterby Marl. Proceedings of the Yorkshire Geological Society 38: 381-424.