Published online by Cambridge University Press: 14 July 2015
Oriostoma bromidensis n. sp., the oldest reported occurrence of Oriostoma Munier-Chalmas, 1876, is described from the Bromide Formation (Middle Ordovician, Blackriverian) of Oklahoma. The species is also the oldest known representative of the family Oriostomatidae Wenz, 1938. It is one of few gastropods known from the Bromide and is smaller than the widespread and abundant Oriostoma typical of the Silurian.