THE EFFACED STYGINID TRILOBITE THOMASTUS FROM THE SILURIAN OF VICTORIA, AUSTRALIA

Thomastus is a blind effaced styginid trilobite that occurs in strata of Wenlock age in Victoria, Australia. The genus is most closely relat ed to Bumastella and Illaenoides, with which it shares characters such as a highly convex cephalon, the absence of the omphalus and the ante rolateral internal pit, a weakly forwardly converging facial suture, a transverse furrow in front of the articulating flange on the posterio r fixigenal margin, and a pygidium with a deep holcos. Of the four spe cies previously assigned to Thomastus, T. collusor and T. vicarius are considered to be synonyms of the type species T. thomastus. One new s pecies, T. aops, is described.