Desmoinesian (Middle Pennsylvanian) radiolarians are described from carbonate concretions found in the black phosphatic facies in strata of the Excello Shale Member of the Fort Scott Limestone (Marmaton Group) in southeastern Kansas (K69 section), USA. Ten new species of radiolarians are described: Albaillella kansaensis, Holdsworthella trifurca, Pseudoalbaillella deformata, Entactinia jayhawkensis, E. heckeli, E. boardmani, Apophysiacus martiali, Moskovistella insolita, Palacantholithus umbrelliformis, and Ormistonella perrara. The Kansas radiolarian assemblage is different from the assemblage described from the Excello Shale of Iowa in the preservation and taxonomic composition. The radiolarians are preserved as pyritized internal molds or regular tests replaced by pyrite, and unidentifiable organic material. The domination of entactinarians and albaillellarians in the Kansas assemblage and their poor to excellent preservation indicate the formation of early diagenetic calcareous concretions in anoxic conditions. The appearance of the spicular radiolarian genus Palacantholithus indicates an influx of relatively cold water connected with upwelling. The Kansas location was much farther offshore (450 km basinward) compared to the Iowa localities suggesting a difference in thermocline depth, affecting water temperature, oxygenation, and nutrients.