Fructification plasmodiocarpous, reticulate, creeping, applanate and generally widely effused, white; the peridium thin, cinereous, covered by a delicate, white, calcareous crust; the columella simply the base of the plasmodiocarp, thin alutaceous; the capillitium pale, consisting of short threads somewhat branched toward their distal extremities; spores smooth, pale violaceous, 8-10 mu. This is _Physarum effusum_ Schw., _vid. N. A. F._, No. 2297. It is reported by Morgan from Ohio, and we have one specimen from eastern Nebraska, so that it is probably of general distribution in the eastern United States. This species was in the previous edition distinguished from the Rostafinskian _P. reticulatum_ with spores a little smaller, 6-8 mu, and with a much stronger tendency to the formation of definite sporangia, elongate indeed and branching but often globose or depressed globose. This we may know as, VAR. RETICULATUM Rost. 1875. _Chondrioderma reticulatum_ Rost., _Mon._, p. 170. 1894. _Diderma reticulatum_ (Rost.) Morg., _Jour. Cin. Soc._, p. 71. Sporangia gregarious, generally rounded, not much depressed, flat, sometimes, especially toward the margin of a colony, elongate, venulose or somewhat plasmodiocarpous, dull white, the inner peridium ashen or bluish, remote from the calcareous crust, which is extremely fragile, easily shelling off; columella indistinguishable from the base of the sporangium, thin, alutaceous; capillitium of short, generally colorless, delicate, sparingly branching or anastomosing threads perpendicular to the columella; spores black in mass, by transmitted light violet-tinted, smooth, 6-8 mu. Perhaps our most common form. Found in fall on dead twigs, leaves, etc. Recognized by its rather large, white, depressed or flattened sporangia tending to form reticulations, and hence suggesting the name. The lines of fruiting tend to follow the venation of the supporting leaf; where the sporangium is round, the columella is a distinct rounded or cake-like body; where the fruit is venulose, the columella is less distinct. By these rounded forms we pass easily, as by a gate, to _D. hemisphericum_, which, when wholly sessile, differs still in greater diameter of the sporangia and in having somewhat larger spores. Usually in such case the compared colony will show somewhere a very short and stout but very real stipe supporting the discoid fruit. Rostafinski divided the genus _Chondrioderma_, i. e. _Diderma_, into three sections:-- _Monoderma_ to include those species in which the calcareous crust is less distinct or connate with the true peridium. _Diderma_, in which the two structures were plainly separate. _Leangium_, used as in the present work. In his first section Rostafinski placed _C. reticulatum_ and _C. michelii_; in the second, _C. difforme_ and _C. calcareum_.