Bathyurid trilobites are one of the most common shallow-marine groups of the Early Ordovician of Laurentia. During the Ordovician, Laurentian North America straddled the Equator, and the current western region formed the northern continental margin. Sampling of secondarily silicified trilobite faunas along this margin in the Great Basin has yielded a wealth of new information, including many dozens of new species of bathyurids. This new knowledge permits an assessment of currently understood natural evolutionary groups within the family. The genus Licnocephala, which in the past has been widely applied, has quite different morphology than has been attributed to it in previous literature. The type species is revised on the basis of new specimens and four new species (two well enough known to formally name) are illustrated. A related new genus, Ibexocephala, includes two new species with highly unusual cranidial morphology involving a sharp posterior change in angle in sagittal (midline) profile. All of the new and revised taxa are Tulean (late Tremadocian, Early Ordovician) in age. They were collected from the Fillmore Formation in western Utah and the Garden City Formation of southeastern Idaho.

Revision of the type species of the Early Ordovician (Tulean, late Tremadocian) bathyurid trilobite Licnocephala Ross, 1951 demonstrates that it has significantly different morphology than that ascribed to it in the earlier literature, which was based largely on species now assigned to a different genus. In addition to the type species, L. bicornuta Ross, 1951, which is fully revised on the basis of new material, four species, all apparently new, have been recovered, two of which, L. ngi n. sp. and L. bradleyi n. sp., are well enough known to formally name. The overall phylogenetic structure of bathyurids is yet to be determined, but several apparent clades can now be recognized and are discussed. Among these is what is termed the “Chapmanopyge group,” including Chapmanopyge Fortey and Bruton, 2013, Punka Fortey, 1979, Uromystrum Whittington, 1953, and Licnocephala. These genera are united in the occurrence of much of the anterior cephalic border on the librigenal anterior projection, with most of the anterior margin of the cranidium representing the suture, the possession of very short (exsag.) strap-like posterior cranidial projections, and extremely narrow visual surfaces. A fifth genus of the group, Ibexocephala n. gen., is represented by two new species, I. lossoae (type species) and I. dekosterae. The taxon features a remarkable cranidial morphology involving a strong deflection of the posteriormost part of the cranidium from the anterior part in sagittal profile.