At least three species of Radiolaria were recovered from the Pierre Shale in Colorado, Kansas, and Wyoming. Dictyomitra multicostata Zittel is the most abundant and widespread form. Associated benthonic foraminifera and abundance patterns of radiolarians suggest peak radiolarian abundances in outer neritic or greater depths during deposition of the Pierre Shale. Future recoveries may allow formation of a Western Interior radiolarian zonation and better define the Cretaceous paleo-oceanography of North America.--Journal abstract.