ABSTRACT: Middle Pennsylvanian (Desmoinesian) foraminifers and a diverse radiolarian fauna are described from carbonate concretions in the black phosphatic facies of the Excello Shale Member of the Mouse Creek Formation (Marmaton Group) from two sections near the towns of Booneville and Medora in south-central Iowa. One new species of foraminifer, Ammobaculites marmatonensis, and nine new species of radiolarians are described: Albaillella mucronulata, Pseudoalbaillella boonevillensis, Ps. excella, Ps. decurvata, Ps. desmoinesiensis, Entactinia dianae, Spongentactinia? incerta, Tetragregnon iowaensis, and Latentidiota medorensis. The assemblage of radiolarians is similar to the assemblage of the Entactinia – Pseudoalbaillella Beds of the upper Moscovian described from Bashkiria, Southern Urals, Russia. Foraminifers and radiolarians are found together with the conodonts Idiognathodus acutus Ellison, Gondolella bella? Stauffer and Plummer, Neognathodus dilatus (Stauffer and Plummer) and Neognathodus roundyi (Gunnell). The latter species is especially useful for correlation of the Excello fauna to other areas in North America and to the International Carboniferous Time Scale.