(Riedel and Sanfilippo, 1970, emend. 1978a)
The top of the zone is defined by the evolutionary transition from Diartus petterssoni to Diartus hughesi and is coincident with the lower limit of the Didymocyrtis antepenultima Zone.
Events included in the zone are:
- Lithopera neotera -> Lithopera bacca
- Tm Stichocorys wolffii *
- Tm Cyrtocapsella japonica; Tm Lithopera thornburgi
- Tm Cyrtocapsella cornuta; Tm Cyrtocapsella tetrapera
- Tm Carpocanopsis cristata
- Bm Phormostichoartus doliolum
- The lower limit of the zone is approximately synchronous with Tm Dorcadospyris alata; Tm Liriospyris parkerae; Bm Cyrtocapsella japonica; Calocycletta virginis ->Calocycletta cladara
The base of the zone is defined by the morphotypic first appearance of Diartus petterssoni and is coincident with the upper limit of the Dorcadospyris alata Zone.
* In some Pacific Ocean samples the morphotypic last appearance of Stichocorys wolffii is below the morphotypic last appearance of Cyrtocapsella cornuta and the morphotypic first appearance of Phormostichoartus doliolum.
Reference slides R 15.1, R 15.2 and R 15.3 from Sample 85-573B-3-CC: R 16.1, R 16.2 and R 16.3 from Sample 85-573B-6-3, 61-63 cm.