Heterorhabdus angustiforatus

Retecapsa angustiforata Black, 1971a

Retecapsa brightonii Black, 1971a

Retecapsa neocomiana BLACK, 1971a

Cretarhabdus octoperforatus Forchheimer, 1972

The detached calyx of the distal process of Heterorhabdus angustiforatus has previously been described as:

Rucinolithus radiatus Worsley, 1971

Hayesites bulbus Thierstein in Roth & Thierstein, 1972

?Discoaster atlanticus Wilcoxon, 1972

Species of Heterorhabdus are constructed of a cretarhabdid pelaga surrounding a large central area spanned by a distinct axial cross that supports a distal process with a large calyx. The inter-cross area is occupied by lateral bars that delimit pores arranged in a single complete concentric cycle. Each quadrant typically contains two pores formed by a single lateral bar, a feature characteristic of Heterorhabdus angustiforatus.

If we focus on the lateral bars, they appear to be of similar robustness and to delimit pores of comparable size.

Heterorhabdus angustiforatus exhibits first-order, slightly greyish-white interference colours. In plan view under crossed polars, the pelaga shows inclined extinction and length-fast (–) elongation.

The last consistent occurrence of Heterorhabdus angustiforatus is recorded at 125.70 Ma, within the Early Barremian.

Black, M. 1971a. Coccoliths of the Speeton Clay and Sutterby Marl. Proceedings of the Yorkshire Geological Society 38: 381-424.

Forchheimer, S. 1972. Scanning electron microscope studies of Cretaceous coccoliths from the Köpingsberg Borehole No. 1, SE Sweden. Sveriges Geologiska Undersökning, Series C. #668, 65: 1-141.

Roth, P. H. & Thierstein, H. R. 1972. Calcareous nannoplankton: Leg 14 of the Deep Sea Drilling Project. Initial Reports of the Deep Sea Drilling Project. 12: 546-559.

Wilcoxon, J. A., 1972. Upper Jurassic-Lower Cretaceous calcareous nannoplankton from the Western North Atlantic Basin. Initial Reports of the Deep Sea Drilling Project, 11: 427-457.

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.