Cores from subsurface Deadwood Formation contain faunas of Arenig age, trilobite Zone E and G, with position of Zone F marked by unfossiliferous sandstone. Gastropod steinkerns predominate, inarticulate brachiopods are common, trilobites are fragmentary and rare, and the gastropod 'Lytospira' ornata n. sp. and the scolecodont Dentinella primaeva n. gen. et sp. are new in Zone E. Zone G has typical trilobite-brachiopod assemblage with few gastropods. New trilobite taxa are Aulacoparia (Praecoparia) wibauxensis n. sp., Aulacoparia (Aulacoparina) impressa n. sp., Ptyocephalus montanensis n. sp., Oculomagnus obreptus n. gen. n. sp., Peltabellia willistoni n. sp., Reubenella rex n. gen. n. sp., Strigigenalis amerada, and Lloydia (Leiostegium) valmyensis n. sp.