Brachiopods of the Suborder Strophomenidina from the Shumway Cyclothem, Mattoon Formation, Virgilian of Illinois

Eleven species of Strophomenidina representing ten genera occur in marine units within the Shumway Cyclothem at its type locality in Effingham County, Illinois. Ten of the eleven species occur in the upper limestone unit and two of these also occur in the lower limestone unit. One species is confined to the black shale unit separating the two limestones. The assemblage suggests the Shumway Cyclothem is Virgilian but that it is no younger than the Oread Limestone of Kansas. Occurrence of a rich marine fauna at this locality provides a datum point approximately half-way between well-developed faunas in the western Midcontinent and the sparse late Pennsylvanian assemblages of the Applachian Basin.