New Pliomerid Trilobite Genus 'Lemureops' from the Lower Ordovician (Ibexian; Tulean, Blackhillsian) of Western Utah, USA

Species of Lemureops gen. nov. (type species: L. kilbeyi sp. nov.) are common members of faunal assemblages from the Psalikilus pikum, Strigigenalis plicolabeona, Carolinites nevadensis and Presbynileus ibexensis trilobite zones in the upper Fillmore Formation of the Ibex area, western Utah. The genus is defined by several striking apomorphies, including a long, subtriangular anterior border; large subtriangular to reniform palpebro-ocular ridges; a wide, shallow, lacunate axial furrow along the glabella; an anteriorly prominent and posteriorly reduced eye socle; and a pygidium with a strongly tapered posterior outline. Lemureops is likely the sister taxon of Pseudocybele Ross, 1951a, but this hypothesis must be tested in a broader phylogenetic context once Pseudocybele is revised and related taxa presently assigned to Hintzeia Harrington, 1957, and Protopliomerella Harrington, 1957, are described and revised. New species in addition to the type are L. willsonpiperi, L. ploogi and L. koppesi; Pseudocybele lemurei Hintze, 1953, is reassigned to Lemureops. Two additional species are new, but insufficiently known for formal naming.