Previously undescribed trilobites associated with microbial patch reefs have been recovered from the Upper Cambrian (upper Steptoean Stage) Ore Hill Limestone Member of the Gatesburg Formation in south-central Pennsylvania. Reefs in the Imler Quarry and Drab-Beaverton measured sections yielded low-diversity assemblages of trilobites that we assign to the uppermost Cliffia lataegenae Subzone of the Elvinia Zone. The faunas are dominated by the catillicephalid Buttsia drabensisWilson, 1951, and include several new taxa that are not known from coeval off-reef facies. Fine-scale correlation between the two sections reveals that the reefs in the Drab-Beavertown section are slightly younger than those at Imler Quarry and represent the youngest Steptoean fauna described from the Appalachian region.
New taxa include Imlerella n. gen. (type species Imlerella praecipita n. sp.), Stittaspis n. gen. (type species Stittaspis loria n. sp.), and Dellea rogersi n. sp. Stigmacephalus? distortaWilson, 1951, is reassigned to Stittaspis and is restricted to the type. Additional material of Buttsia drabensis illustrates features not discernible in previous treatments of this variable species.