(Riedel and Sanfilippo, 1970, emend. Foreman, 1975)
The top of the zone is defined by the morphotypic first appearance of Sphaeropyle langii and is coincident with the lower limit of the Sphaeropyle langii Zone. The top of the zone is redefined by Foreman (1975) for the North Pacific where the tropical Spongaster pentas Zone cannot be recognized.
The base of the zone is defined by the earliest evolutionary appearance of Stichocorys peregrina and is coincident with the upper limit of the Didymocyrtis penultima Zone.
Subsequent unpublished studies (Kling, pers. comm., 1992) and our own observations suggest that Sphaeropyle langii and Sphaeropyle robusta are not stratigraphically useful species and that the radiolarian zonation in this part of the time scale will need to be revised.
Although equivalent to the low-latitude zone of the same name, the aspect of the fauna in middle latitudes is often different and important marker species are frequently missing.
Reference slides R 55.1, R 55.2 and R 55.3 from Sample 32-310-7-5, 63-70 cm.