Four cheirurine trilobite species belonging to three closely related genera are described from the Middle Ordovician Bobcaygeon Formation (Rocklandian–Kirkfieldian) of the Lake Simcoe area in south-central Ontario. Bufoceraurus is a new genus characterized by its large size, profuse, wart-like tubercles over the entire exoskeleton, short posterior border spines on the cephalon, short thoracic pleural spines, and large pygidium with two pairs of prominent posterior spines. The genus is represented by Bufoceraurus bispinosus (Raymond and Barton 1913). Gabriceraurus hirsuitus (Ludvigsen 1979b), Ceraurus plattinensis Foerste, 1920, and Ceraurus cf. globulobatus Bradley, 1930 are other species documented. Complete dorsal exoskeletal reconstructions are presented for all species based on well-preserved material. Hypostomes are known for all species.