Braarudosphaera stylifera Troelsen & Quadros, 1971 (Fig. 18 A-D)

Braarudosphaera stylifera Troelsen & Quadros, 1971: 212, pl.1, figs 8-14.

DISTRIBUTION. — This taxon is recorded in several middle Eocene outcrop and borehole sections in Belgium (Steurbaut in Herman et al. 2001 and in Smith et al. 2004; Steurbaut et al. 2015). In the Mont-des-Récollets section it consistently ranges from the uppermost part of the Brussel Sand Formation (base of Unit B4) to the base of the Wemmel Sand Member. In terms of calcareous nannoplankton zones, its occurrence encompasses the upper part of NP14 and the lower part of NP15, as it appears to do in the Paris Basin (Aubry 1983, 1986) and the Aquitaine Basin (Lin et al. 2017). In the Paris Basin it seems to recur in the Bartonian (Chavençon Marls: NP17 or NP18, Aubry 1983: pl. 8, figs 10-11), although this has not been observed in the other basins.

DISCUSSION

B. stylifera differs from all up to now known Braarudosphaera taxa by its very high slightly tapering outline, resembling a pentagonal pyramid with truncated top, the margin sides of which are often slightly bowed inward (Fig. 18B). Both pentagonal ends can clearly be observed viewed from above when over-focusing and under-focusing with the microscope.