Sporangia gregarious, depressed-globose, umbilicate below, whitish or gray, small, about 1/2 mm., stipitate; stipe erect, rather slender, black, faintly striate, about equal to the sporangium in the horizontal diameter; columella distinct, dark brown, globose or depressed-globose, attaining in some cases the centre, rough; capillitium delicate, almost colorless, radiating, sparsely branched; spores in mass dark brown, by transmitted light violet-tinted, minutely roughened, 8-10 mu. Probably more common than the preceding, and generally mistaken for it. Distinguished by its smaller size, longer and more slender stem, and general trim, well-differentiated appearance. Certainly very near the preceding, of which Mr. Lister regards it as merely a variety. Professor Morgan thought it in this country the more common form. New York, Ohio, Iowa; reported from Europe, Africa, South America. 9. DIDYMIUM CLAVUS (_Alb. & Schw._) _Rabenhorst._ 1805. _Physarum clavus_ Alb. & Schw., _Consp. Fung._, p. 96. 1829. _Didymium melanopus_ Fries, _Syst. Myc._, III., p. 114. 1844. _Didymium clavus_ (Alb. & Schw.) Rabh., _Ger. Cr. Fl._, No. 2282. 1875. _Didymium clavus_ (Alb. & Schw.) Rost., _Mon._, p. 153. 1899. _Didymium clavus_ (Alb. & Schw.) Rabenh., Macbr., _N. A. S._, p. 90. 1911. _Didymium clavus_ Rost., List., _Mycet., 2nd ed._, p. 128. Sporangia gregarious, pale gray, discoid or pileate, depressed, stipitate; the peridium dark-colored, frosted with calcareous crystals above, naked below; stipe short, slender, tapering upward, furrowed, arising from a hypothallus more or less distinct, black; columella obsolete; capillitium of delicate threads, pale or colorless, little branched; spores violaceous, pale, nearly smooth, 6-8 mu. This species is well differentiated, easy of recognition by reason of its peculiar discoid sporangium, calcareous above, naked and black beneath. _D. neglectum_ Massee, reported from Philadelphia, is said to be a slender form of the present species. The figures of _D. clavus_ by Albertini and Schweinitz are excellent, as also the description. Not common. Pennsylvania, Ohio, Iowa. 10. DIDYMIUM NIGRIPES (_Link_) _Fries._ PLATE VII., Figs. 2, 2 _a_, 2 _b_. 1809. _Physarum nigripes_ Link, _Obs. Diss._, I., p. 27. 1818. _Physarum microcarpon_ Fr., _Sym. Gast._, p. 23. 1829. _Didymium nigripes_ (Link) Fr., _Syst. Myc._, III., p. 119. 1875. _Didymium microcarpon_ (Fr.) Rost., _Mon._, p. 157. 1896. _Didymium microcarpon_ Fr., Morg., _Jour. Cin. Soc._, p. 61.