The trilobites Mitroplax gen. nov. and Spiniscutellum (Scutelluidae) from the Lower Devonian of Victoria, Australia

The new scutelluid trilobite genus Mitroplax, with type species M. enormis (Etheridge, 1894), occurs in Pragian to early Emsian strata at several localities in Victoria, Australia. The genus is characterized by a remarkably long and flat anterior cephalic border, a glabella that expands almost uniformly forward from the occipital furrow, a subcircular S2 discrete from S1, and a pygidium with the well-rounded paired pleural ribs and the posterior bifurcations of the postaxial rib tapering almost to a point distally. The type species grew to exceptional size, as indicated by the dimensions of the largest pygidia. Another scutelluid from the Lochkovian of Victoria, 'Goldius' greenii Chapman, 1914, is revised and assigned to Spiniscutellum Snajdr, 1960. This species and a related one from the Lochkovian of the Bungonia district of south-eastern New South Wales are the first records of Spiniscutellum from eastern Gondwana. Spiniscutellum (Lochkovopeltis) Horbinger, 2004 is regarded as a junior synonym of Spiniscutellum.