SUMMARYThe genusGuttulinopsisof E. W. Olive is briefly reviewed and the common coprophilous speciesG. vulgarisis considered with regard to its distinguishing characteristics, the development of its fructifications (sorocarps) and its cultivation in the laboratory upon sterile dung partially embedded in low-nutrient agar. More detailed attention is given to the new speciesG. niveathat differs from the older species in important particulars: it produces sorocarps with well defined cellular stalks (sorophores) of a characteristic tapered pattern; it bears globose to subglobose spore heads (sori) that are consistently snow white when young, becoming lightly pigmented with age; and it can be cultivated quite successfully in two-membered cultures with eitherKlebsiella pneumoniaeorEscherichia coliupon relatively weak glucose-peptone agar buffered to slightly acid pH. The myxamoebae ofG. nivea, like those ofG. vulgarishave lobose pseudopodia, nuclei (usually single) with centrally positioned nucleoli, usually single contractile vacuoles, and spores that often show prominent crescent-shaped vacuolation situated just inside the spore wall. Cell aggregation inG. nivealeading to sorocarp formation, as inG. vulgaris, occurs without stream formation, the converging myxamoebae responding individually to some chemotactic attractant of unknown nature.