Significance of a Late Ordovician Triarthrus (Trilobita, Olenidae) from New South Wales, Australia

Triarthrus novoaustralis, a new species of olenid trilobite, is described from the Malachis Hill Formation (mid-Katian, Late Ordovician) near Keenans Bridge and Canobolas State Forest, west of Orange, New South Wales, Australia. This is the second named (and youngest) olenid occurrence from the entire Ordovician of eastern Gondwana. Additionally, its recognition enables revised stratigraphic correlation and enhanced biostratigraphic constraint of the upper Keenans Bridge section to the pre-Paraorthograptus pacificus graptolite Zone of early Bolindian age, based on the co-occurrence of Triarthrus with age-diagnostic graptolites from Canobolas State Forest.