(Riedel and Sanfilippo, 1970, emend. 1978a)
The top of the zone is defined by the evolutionary transition from Spongaster berminghami to Spongaster pentas and is coincident with the lower limit of the Spongaster pentas Zone.
Events included in this zone are:
- Bm Botryostrobus aquilonaris; Tm Siphostichartus corona; Bm Pterocorys campanula
- Tm Acrobotrys tritubus; Tm Calocycletta caepa
- Tm Stichocorys johnsoni
- Tm Calocycletta cladara
The base of the zone is defined by the evolutionary transition from Stichocorys delmontensis to Stichocorys peregrina and is coincident with the upper limit of the Didymocyrtis penultima Zone.
The upper part of this zone is equivalent to Zone NR11 (Anthocyrtidium prolatum Nigrini and Caulet, 1988, p.355, pl.2, figs.7-10) as defined by Johnson et al., 1989 for the tropical Indian Ocean.
The Miocene-Pliocene boundary lies within this zone.
Reference slides R 7.1, R 7.2 and R 7.3 from Sample 85-573-10-CC; R 8.1, R 8.2 and R 8.3 from Sample 85-573-12-CC; R 9.1, R 9.2 and R 9.3 from Sample 85-573-13-4, 65-66 cm.