Nodular limestone strata in the lower part of the Kinderhookian [Mississippian] Sappington sandstone of southwestern Montana contain a spongiostromatid algae and sponge association that would suggest a shallow water algal bank environment. Fossil sponges of the genus Scaphiomanon, n. gen., which includes 2 species, Scaphiomanon nodulosum, n. sp., and Scaphiomanon hadros, n. sp., are described from this zone. Similar nodular limestone beds are also present in the Leatham formation of the Logan, Utah area and the Midridge limestone of the Confusion Range, Utah.