This genus is distinguished from _Physarum_ and _Badhamia_ chiefly by the form of the sporangia and the method of dehiscence. The capillitium is in some specimens particularly, of the _Physarum_ type; in others, like that of _Badhamia_. There are accordingly species that receive at the hands of different authors diverse generic reference as one feature or another in the structure is emphasized in the different cases. It is granted that it is hard to draw the line sometimes between forms in which the dehiscence is irregularly circumscissile and those in which the wall breaks without any regularity whatever, since, in all, the breaking up of the peridium usually begins at the top. Species here included will, however, offer little ambiguity. =Key to the Species of Craterium= A. Dehiscence circumscissile or by the breaking up of the upper wall of the sporangium. _a._ Sporangia violet or purple 1. _C. paraguayense_ _b._ Sporangia yellow 2. _C. aureum_ _c._ Sporangia white-capped. 1. Sporangia obovoid or globoid 3. _C. leucocephalum_ 2. Sporangia cylindric, elongate 4. _C. cylindricum_ B. Dehiscence by a distinct lid. _a._ Capillitium pale brown 5. _C. concinnum_ _b._ Capillitium white 6. _C. minutum_ 1. CRATERIUM PARAGUAYENSE (_Speg._) _List._ 1883. _Didymium paraguayense_ Speg., _Fung. Guar. Pug._, 1, p. 141. 1893. _Craterium rubescens_ Rex, _Proc. Philad. Acad. Nat. Sci._, p. 370. 1894. _Craterium rubescens_ Rex, List., _Mycetozoa_, p. 71. 1899. _Craterium rubescens_ Rex, Macbr., _N. A. S._, p. 75. 1904. _Iocraterium paraguayense_ (Speg.) Jahn, _Hedwigia_, XLII., p. 302. 1911. _Craterium paraguayense_ List., _Mycetozoa, 2nd ed._, p. 95. Sporangia gregarious, cylindrical or elongate cyathiform, stipitate, dark violet-red, the apex slightly roughened by pale calcareous granules, the peridium longitudinally wrinkled below; dehiscence, irregularly circumscissile; stipe darker, one-half the height of the sporangium, longitudinally wrinkled; capillitium dense, abundantly calcareous; spores violet-brown, minutely roughened, 7-8 mu. In form resembling the following species, but instantly distinguished by the color, which is red throughout, tinged with purple or violet. The capillitium is badhamioid, as noted by Dr. Rex. Very distinct from _P. newtoni_ in color, form, habit, epispore, etc. 2. CRATERIUM AUREUM (_Schum._) _Rost._ 1803. _Trichia aurea_ Schum., _Enum. Pl. Saell._, II., p. 207. 1829. _Craterium mutabile_ Fries, _Syst. Myc._, III., p. 154. 1875. _Craterium aureum_ (Schum.) Rost., _Mon._, p. 125.