It will be said, has been said, was said by Fries, that these variations are insignificant, "pendent ex aeris constitutione"; but as a matter of fact the several types now in question may be found on the same day, so that evidently something other than the atmospheric environment must determine. Again it is said that the differences are in external form or color only, the spores in all cases almost if not quite the same. This is true; but specific characters are _surface_ characters in fact: a species morphologically is merely the form in which a _kind_ or _genus_ presents itself. If the presentation be constant, for our convenience we say so, in bestowing a name. Whether in our present treatment the convenience is purely personal, students may decide. However it all may be, there are in this part of the world many varying presentations of _Fuligo_ capable of illustration and description; the same forms, perhaps, which have attracted the notice of the more acute mycologists in the older history of the subject. Some of these forms we here venture to describe, with such annotation as may show something of present knowledge. =Key to the Species of Fuligo= _A._ Aethalium 1 cm. or less; spores spherical 1. _F. muscorum_ _B._ Aethalium larger, or plasmodiocarpous, even sporangi-form, crust white, smooth, even, spores elliptical 2. _F. cinerea_ _C._ Aethalia larger, 2 cm. or more. 1. Cortex yellow, etc., not white; spores 6-8 mu 3. _F. septica_ 2. Cortex nearly or quite wanting; spores 10-12 4. _F. intermedia_ 3. Cortex white, a foamy crust; spores 15-25 5. _F. megaspora_ 1. FULIGO MUSCORUM _Alb. & Schw._ 1894. _Fuligo muscorum_, Alb. & Schw. Lister, _Mycetozoa_, p. 67. 1875. _Licea ochracea_ Peck, N. Y. _Rep._, XVIII., p. 55. 1879. _Fuligo ochracea_ Peck, N. Y. _Rep._, XXXI., p. 56. 1894. _Fuligo muscorum_, Alb. & Schw., Lister, _Mycetozoa_, p. 67. 1911. _Fuligo muscorum_ Alb. & Schw., Lister, _Mycetozoa, 2nd ed._, p. 87. Plasmodium orange-yellow. Aethalium globoid, very small, 1 cm. or less, the cortex very thin, greenish yellow; sporangial walls not evident; capillitium well-developed, the numerous calcareous nodes fusiform or often branching, and connected by rather short, transparent internodes; spores coarsely warted, 10-11 mu. This form seems to differ from _F. septica_ chiefly in its constant diminutive habit of fruiting, in its delicate cortex, and in its spores, brighter, larger, and more coarsely warted. The descriptions and figure by Schweinitz seem referable to nothing else. First reported by Albertini and Schweinitz from Germany; by Schweinitz from the Carolinas; then by Dr. Peck described as a _Licea_ from New York. It seems less commonly collected in the United States. 2. FULIGO CINEREA (_Schw._) _Morg._ PLATE X., Figs. 3, 3 _a_, and 3 _b_, and Plate XXIII.