The Scleractinian genus Actinacis. Systematic revision and stratigraphic record of the Tertiary species with special regard to Italian occurrences.

Twenty-seven Tertiary species belonging to the cosmopolitan reef-building scleractinian genus Actinacis, have been described in the literature. A detailed systematic revision has been carried out for Italian and European species by thin section measurements. A combination of several measured corallite morphologic characters and diagnostic features is proposed as a realiable tool for species recognition. Preliminary examination of the stratigraphic and geographic distribution of Actinacis species suggests that: 1) the Tertiary distribution of the genus ranges from the Late Paleocene to the Late Oligocene; 2) the highest species diversity occrred during the Middle Eocene, when the genus consisted of a relatively large number of geographically restricted species; 3) only two widespread species survived the Eocene/Oligocene turnover and reached the Late Oligocene, when the genus became globally extinct.