(Foreman, 1973, emend. Riedel and Sanfilippo, 1978a)
The top of the zone is defined by the evolutionary transition from Theocotyle nigriniae to Theocotyle cryptocephala and is coincident with the lower limit of the Theocotyle cryptocephala Zone.
Events included in the zone are:
- Spongatractus balbis -> Spongatractus pachystylus
- Tm Lamptonium sanfilippoae
- Bm Thyrsocyrtis rhizodon
- Bm Podocyrtis diamesa
- The lower limit of the zone is approximately synchronous with Bm Lamptonium fabaeforme constrictum; Phormocyrtis striata exquisita -> Phormocyrtis striata striata; Bm Podocyrtis acalles; Tm Phormocyrtis cubensis; Bm Lychnocanoma bellum
The base of the zone is defined by the morphotypic first appearance of Theocorys anaclasta and is coincident with the upper limit of the Buryella clinata Zone.
Reference slides R 46.1, R 46.2 and R 46.3 from Sample 10-94-28-1, 110-117 cm.