(Riedel and Sanfilippo, 1970, emend. 1971)
The top of the zone is defined by the morphotypic first appearance of Diartus petterssoni and is coincident with the lower limit of the Diartus petterssoni Zone.
Events included in the zone are:
- Lithopera renzae -> Lithopera neotera
- Didymocyrtis mammifera -> Didymocyrtis laticonus
- Bm Lithopera thornburgi; Bm Phormostichoartus corbula; Bm Dictyocoryne ontongensis
- Tm Calocycletta costata; Tm Didymocyrtis tubaria; Tm Didymocyrtis violina; Bm Lithopera renzae
- The lower limit of the zone is approximately synchronous with Tm Dorcadospyris forcipata
The base of the zone is defined by the evolutionary transition from Dorcadospyris dentata to Dorcadospyris alata and is coincident with the upper limit of the Calocycletta costata Zone.
Reference slides R 17.1, R 17.2 and R 17.3 from Sample 85-573B-9-2, 61-63 cm; R 18.1, R 18.2 and R 18.3 from Sample 85-573B-10-3, 61-63 cm.