'Prosopiscus' (Ordovician; Trilobita) from the Rowena Formation, western New South Wales

'Prosopiscus tatei' is documented from the Rowena Formation (Mutawintji Group) in the Bynguano Range, western New South Wales. The occurrence of this species in the basal Stairway Sandstone in the Amadeus Basin, Northern Territory, has enabled a more precise age determination of the middle part of the Rowena Formation, equivalent to the 'Histiodella holodentata' Zone within the early Darriwilian Stage of the Middle Ordovician. This new biostratigraphic information also demonstrates that 'Prosopiscus' persisted on the Gnalta Shelf of western New South Wales from the late Early Ordovician (Bendigonian-Chewtonian) to the Middle Ordovician (Darriwilian).