Trilobites from theCedarina dakotaensisZone, lowermost part of the Deadwood Formation (Marjuman Stage, Upper Cambrian), Black Hills, South Dakota

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Abstract
Trilobites assigned to 14 genera and 14 species are reported from basal part of the Deadwood Formation in the Black Hills of South Dakota. Six additional taxa are left in open nomenclature. One new species,Cedarina dakotaensis, is described. These trilobites are assigned to a new zone, theCedarina dakotaensisZone, named after the most abundant trilobite species.Species ofCedarinaandModociaare the most abundant in theCedarina dakotaensisZone, accompanied by less common specimens of species ofArapahoia, Menomonia, Hardyoides, Welleraspis, Kormagnostus, andKingstonia. Cedarina dakotaensisandModocia centralisare the most abundant species in the nearshore sandstone lithofacies, whereasArapahoia spatulatais the predominate taxon in the offshore limestone lithofacies.The fauna of theCedarina dakotaensis Zone(which lacks species ofCedaria) occupies the biostratigraphic interval of the traditionalCedariaZone of the Marjuman Stage. Trilobites from theCedarina dakotaensisZone can be used to correlate the basal part of the Deadwood with coeval strata elsewhere in North America.