(Nigrini, 1971, who termed it an 'Assemblage Zone')
The top of the zone is defined by the morphotypic first appearance of Collosphaera tuberosa and is coincident with the lower limit of the Collosphaera tuberosa Zone.
Events included in the zone are:
- Tm Pterocorys campanula
- Bm Pterocorys hertwigii
The base of the zone is defined by the morphotypic last appearance of Anthocyrtidium angulare and is coincident with the upper limit of the Anthocyrtidium angulare Zone.
Reference slides R 3.1, R 3.2 and R 3.3 from Sample 85-573-2-CC.