Its middle and upper Miocene upwelling-rich assemblages, and its unique highly siliceous rocks from diatom-rich plankton, became diatomites, porcelainites, and banded cherts.
It contains only one species, Prohepialus incertus, which was described from a Thanetian crater lake diatomite (Paleocene) in Menat (Puy-de-Dôme), France.