This most common species seems to be also the center of widest differentiation. In a valuable paper on the Myxomycetes of Dr. C. H. Peck's Herbarium Dr. Sturgis points out the varying relationships of a group of surrounding forms. According to account _C. nigra_ verges on one side to _C. laxa_, on the other to _aequalis_ which the Listers enter as varietal here. However, in the former the more rigid, direct and simple branching from the columella is usually determinative; in the latter the color, form, and generally more delicate structure, and a tendency to grow in tufts will serve to distinguish. In this discussion we have assumed as typical the globose sporangium, with the variations in the direction of ovate, obovate, ellipsoidal, etc., the capillitium flexuous and more richly anastomosing near the columella. On the drier slopes in the mountains of Colorado specimens are especially abundant, in proper season covering apparently the lower surface of every barkless twig or fallen stem or _tree entire_! In such a field one might imagine every possible variation open to observation. Probably such is the case; but as a matter of fact a single small plasmodium at lower levels will sometimes show greater range of variation than were noted on the mountain-side. The cylindric forms were for some reason few, and when noted were short, though often surmounting stems of double the usual length. Rostafinski calls this _C. friesiana_, a name suggested by De Bary. By this name the species was commonly known for many years. More recently some writers prefer _C. obtusata_ Preuss; but _C. obtusata_ Preuss, as figured by that author (Sturm's _Deutsch. Fl._, Pl. 70), is surely more likely _Enerthenema papillata_, and the author says in his description "capillitio vertice soli innato." Persoon certainly recognized the species, and his description, though brief, is yet applicable to no other European species. There seems no reason why the name he gave should not be permanently adopted. Rostafinski's figure, Tab. XIII., shows an ellipsoidal sporangium, not cylindric. On the lower levels of the Mississippi valley, the species is not common. Possibly overlooked by reason of its minuteness. Massachusetts, Pennsylvania, Ohio, Iowa, Colorado, North Carolina, Missouri. 9. COMATRICHA AEQUALIS _Peck._ PLATE VI., Figs. 3, 3 _a_, 3 _b_, 3 _c_, 3 _d_; and PLATE XVIII., Figs. 13, 13 _a_, 13 _b_. 1890. _Comatricha equalis_ Peck., _Rep. N. Y. Mus._, XXXI., p. 42.