The trilobite fauna of the middle Silurian (Telychian to possibly earliest Sheinwoodian) Tomcat Creek limestone in the Broken River Province of north Queensland is dominated by the suborder Illaenina, including illaenimorphs (Illaeninae and Bumastinae) and members of the Scutelluidae. Scutelluidae are most diverse, with eight genera, of which Dolabrapex, Iotoryx, Perizostra, and Quintonia are new. Perizostra is the first scutelluid with a cephalon that may be described as of phacomorph appearance. Illaenimorphs are represented by three genera, including Opsypharus, which is regarded as a senior synonym of Paracybantyx but distinct from Failleana with which it has been placed in synonymy by some authors. Thirteen species are new: Cybantyx? ergodes, Opsypharus pandanensis, Australoscutellum talenti, Dolabrapex acomus, Illaenoscutellum psephos, Iotoryx clarksoni, Japonoscutellum mawsonae, J. drakton, J. fractum, Kosovopeltis avita, Perizostra campbelli, Quintonia arata, and Q. pavo. A species of Stenoparia is placed in open nomenclature. The species of Australoscutellum, Illaenoscutellum, and possibly Kosovopeltis are the oldest known representatives of those genera. These genera and Japonoscutellum are also common in faunas from limestones of Wenlock to Ludlow age in central western New South Wales, reflecting the similarity in lithofacies. The monotypic Late Ordovician genus Craigheadia, which has been regarded as a scutelluid, belongs to the Lichidae and is probably a junior synonym of Leiolichas.