(Riedel and Sanfilippo, 1970, emend. 1978a)
The top of the zone is defined by the morphotypic last appearance of Diartus hughesi and is coincident with the lower limit of the Didymocyrtis penultima Zone.
Events included in the zone are:
- Tm Dictyocoryne ontongensis; Bm Acrobotrys tritubus; Tm Botryostrobus miralestensis
- The lower limit of the zone is approximately synchronous with Didymocyrtis laticonus -> Didymocyrtis antepenultima
The base of the zone is defined by the evolutionary transition from Diartus petterssoni to Diartus hughesi and is coincident with the upper limit of the Diartus petterssoni Zone.
Reference slides R 12.1, R 12.2 and R 12.3 from Sample 85-573-17-3, 61-62 cm; R 13.1, R 13.2 and R 13.3 from Sample 85-573-17-CC; R 14.1, R 14.2 and R 14.3 from Sample 85-573-18-CC.