The new Ordovician genus Hillophyllum and the early history of rugose corals with Acanthine Septa

Two species of the new rugose coral genus Hillophyllum are described from Ordovician limestones of central‐western New South Wales. The larger species, H. priscum sp. nov., is the earliest rugosan to be found in New South Wales successions, first appearing in horizons of probable Gisbornian age (about middle Lower Caradocian), and seems to be the earliest record of a solitary to fasciculate species exhibiting monacanthine septa. A smaller species, H. sp., occurs with H. priscum and the first species of Palaeophyllum in higher horizons, of probable Lower Eastonian age (approximately upper Lower Caradocian). The history of the Ordovician rugose corals exhibiting acanthine septa is reviewed. Hillophyllum shows relationships with the massive, cerioid rugose species of Foerstephyllum type, and with the solitary, non‐tabulated Lambeophyllum, Coelostylis, and Primitophyllum. Together they appear to be the earliest representatives of the Suborder Cystiphyllina.