The current classification of the Proetidae is completely inadequate for the sensible assignment of trilobites from the lower Mississippian of North America. This results from unclear discrimination of established genera and from the existence of a far greater variety of morphological types than can be accommodated in so few genera. This paper, the first of 2 whose aim is to bring the systematics of North American proetids up to date, considers genera which represent evolutionary lines that did not survive the middle Osage. All existing species which are considered valid are redescribed. The previously described or inadequately described trilobite faunas the Chouteau (of Knox Co., Mo.), Chappel, Welden, Darty, and Lake Valley limestones are included.