The Conococheague formation of the Cumberland-Shenandoah valleys of Pennsylvania, Maryland, and Virginia was known to represent most of the Croisian series, but only a few Franconian and 2 Trempealeauian fossils had been published. A faunule of Trempealeauian age including 15 species is described from the upper Conococheague of Pennsylvania and Maryland. The Frederick limestone of Maryland yielded 19 species of Trempealeauian trilobites, of which only one was previously known from the formation. The overlying Grove limestone, hitherto considered entirely Lower Ordovician on the basis of brachiopods and cephalopods collected in the upper part of the formation, yielded a faunule of 11 Trempealeauian trilobites near the base, indicating that the Cambrian-Ordovician boundary lies within the formation. All these faunules have many genera and species in common with the Hungaia magnifica boulders at Levis, Quebec, the Gorge formation of northwestern Vermont, and the Eminence dolomite of the Ozark uplift. One new genus, Conococheaguea (type species: C. ovata, n. sp. ) and the following new species are described: Apatokephaloides macrops, A. minor, Aposolenopleura plicata, Bowmania pennsylvanica, Keithia intermedia, Idiomesus intermedius, Levisella nasuta, Prosaukia corrugata, Richardsonella subcristata, and Triarthropsi limbata.