The two new sponges, Diagonodictya crusta n. gen. and sp., a small steeply obconical, dictyospongiid hexactinellid, and Pohlispongia monosphaera n. gen and sp., a spheroidal, single-chambered, monaxonid demosponge—along with several isolated hexactinellid spicules—are described from low-energy, low pH, black shales within the Pennsylvanian Desmoinesian Carbondale Formation from northwestern Illinois, from the Illinois Basin. They are associated with a variety of small fossils, which range from radial and spheroidal to lobate obconical, here identified only as forms A and B, that are possible spore-bearing organs of plants. Some of these latter forms occur as core debris associated with fine hexactine-derived sponge spicules and bivalve? fragments in fecal pellets. The described assemblage may have lived as pelagic organisms in a protected environment and may have been deposited under swamp “flotants” in anoxic shallow water conditions. Alternatively, the assemblage may have lived as part of an open water pelagic biota, ending up in death in anoxic, deeper water environments.