A REVISION OF ACTINODICTYON PANTOCSEK

Actinodictyon Pantocsek is a genus of the Heliopeltaceae with alternately raised and depressed sectors and rimoportulae with a unique structure; their external openings are at the distal ends of the raised sectors and their internal openings are appreciably proximal to these, the two being connected by a narrow tube. There are six species, two of which have been described as species of Actinodiscus Greville and one as the sole species of the monotypic genus Anthemodiscus Barker & Meakin. One species, Actinodictyon fergusonii Ross & Sims is described as new. Three species occur in the late Cretaceous, all surviving into the Paleogene, two others occur only in the Paleogene, and one species is known only from the Miocene, or perhaps also the early Pliocene.