(Riedel and Sanfilippo, 1970, emend. 1978a, emend. Sanfilippo et al.,1985)
The top of the zone is defined by the morphotypic last appearance of Pterocanium prismatium and is coincident with the lower limit of the Anthocyrtidium angulare Zone. This zonal boundary is approximately equivalent to the Pliocene-Pleistocene boundary.
Events included in the zone are:
- Bm Anthocyrtidium angulare
- Tm Theocorythium vetulum
- Bm Lamprocyrtis neoheteroporos
- Bm Theocorythium trachelium trachelium
The base of the zone is defined by the morphotypic last appearance of Stichocorys peregrina and is coincident with the upper limit of the Stichocorys peregrina Zone.
The suggested use of the evolutionary transition from Lamprocyrtis neoheteroporos to L. nigriniae (formerly L. haysi) to define the top of this zone (Riedel and Sanfilippo, 1978a) has proven to be unsatisfactory. That event is commonly no more reliably recognizable than the morphotypic top of P. prismatium, and it frequently occurs as high as the Amphirhopalum ypsilon Interval-zone. Therefore we revert to using the morphotypic top of P. prismatium, which coincides with the lower limit of the Anthocyrtidium angulare Interval-zone. (Sanfilippo et al., 1985)
* In the tropical Indian Ocean, Johnson et al. (1989) used the upper limit of Anthocyrtidium jenghisi (Streeter, 1988, p.63, pl.1, figs.1-4) to divide this zone into two zones, Pterocanium prismatium (NR6) and Anthocyrtidium jenghisi (NR7).
Reference slides R 5.1, R 5.2 and R 5.3 from Sample 85-572-5-3, l30-131 cm.