Sporangia small, scattered, annulate, not only without columella but perforate when the stipe is broken, umbilicate above and below, grey, coated with crystalline frustules, opening irregularly about the periphery; stipe white, or pallid, fluted, tapering upward from a distinct hypothallus; capillitium scanty consisting of delicate, sparsely branching threads, the branchlets anastomosing more or less at length, attached to the peridial wall, radiating from the rim of the slightly depressed top of stipe, without special thickenings save at the insertion of the ramules a triangular enlargement is usual and of dark or pallid shade; spores smooth; however they show three or four spots on the hemisphere and other minute but variable markings; 9-10 mu. Seattle, Washington. Differs from _D. nigripes_ in color of the stipes, capillitium, spore-diameter, etc. 15. DIDYMIUM DUBIUM _Rost._ 1875. _Didymium dubium_ Rost., _Mon._, p. 152. 1892. _Didymium listeri_ Mass., _Mon._, p. 244. 1894. _Didymium dubium_ Rost., List., _Mycetozoa_, p. 95. 1911. _Didymium dubium_ Rost., List., _Mycetozoa, 2nd ed._, p. 126. Fructification wholly plasmodiocarpous, snow-white, small, 2-6 mm., flat and thin; the outer wall double, membranous within, calcareous-crystalline without; columella none; capillitium simple of rather thick, vertical, brown threads, sparingly united laterally, and only occasionally furcate at the ends, especially above; spores minutely spinulescent, violaceous pale, 12-15 mu. Massee thought English specimens out of harmony with the original description and gave them a new name. To refuse this, Lister enlarges the range of spore-measurements and disregards some of Rostafinski's specifications as to capillitium. Our specimens are as described. Bohemia. England. Shores of Lake Okoboji, Iowa. This is indeed a doubtful form. It differs from _D. difforme_ chiefly in that the outer calcareous shell is not smooth, but is covered with abundant loose crystals, frosted. The spores are paler but about the same size. The frosting may be incident to local climatic conditions at the time and place of desiccation. 16. DIDYMIUM DIFFORME _Duby._ 1797. _Diderma difforme_ Pers. _Tentamen Disp. Meth._, p. 19. 1830. _Didymium difforme_ Duby., _Bot. Gall._, ii., p. 858. 1875. _Chondrioderma difforme_ Pers., Rost., _Mon._, p. 177. 1894. _Didymium difforme_ Duby., List., _Mycetozoa_, p. 94. 1899. _Diderma personii_ Macbr., _N. A. S._, p. 96. 1911. _Didymium difforme_ Duby., List., _Mycetozoa, 2nd ed._, p. 124. Plasmodiocarpous, the smooth, white outer peridium separable from the thin, colorless or purplish inner layer; capillitium of rather coarse, flat, dichotomously branching threads, broader below; spores minutely warted, or almost smooth, dark brown, 12-14 mu.