Revision of Acheilus and Theodenisia (Late Cambrian, Trilobita)

Acheilus Clark, 1924, is a kingstoniid trilobite, not a catillicephalid or an unrecognizable genus as previously thought. The catillicephalid Theodenisia Clark, 1948, is here restricted to those species in which the axial furrows terminate at the 4s furrow and which lack a preglabellar furrow. Peracheilus n. gen. is proposed as a replacement name for the catillicephalid Acheilus Raymond, 1924. It includes those species previously assigned to Theodenisia in which the axial furrows continue past the 4s furrow to join a narrow preglabellar furrow. Acheilus, Theodenisia, and Peracheilus occur in the Late Sunwaptan of North America; Theodenisia also occurs in the early Ibexian.