This species is not common. From Colorado we have fine specimens typical in every way. Specimens from Washington are flat so far as at present at hand; probably represent _D. deplanatum_ (R.) List., which the last named author regards as varietal of the present species, entering it and _D. lyallii_ as sub-species 2 and 1 respectively. _D. deplanatum_ may perhaps be best so disposed of; but _D. lyallii_ is distinguished at sight, as well as by microscopic characters, spores nearly twice as great, rougher and different in color. 9. DIDERMA CINEREUM _Morg._ 1894. _Diderma cinereum_ Morg., _Myx. Mi. Val._, p. 70. Sporangia gregarious, more or less crowded or even confluent, sub-globose, only slightly depressed, ashen white; the peridium not obviously double, very smooth and thin, rupturing irregularly; hypothallus an indistinct membrane or wholly wanting; columella large, globose or hemispheric, white, the surface granulose; capillitium of very slender colored threads, the extremities pellucid, more or less branched; spores violaceous, minutely warted, 9-11 mu. Growing on old wood, leaves, etc. The sporangium .3-.5 mm., thin and smooth or rugulose. This elegant little species I know only from specimens received from Mr. Morgan. It seems to be closely related to _D. spumarioides_, from which it is distinguished by its color, darker, and its smoother, or less spinulose spores. The author compares the color and external appearance to that of _P. cinereum_,--_Jour. Cin. Soc._, XVI., p. 154. Ohio, Pennsylvania. 10. DIDERMA HEMISPHERICUM (_Bull._) _Horne._ 1791. _Reticularia hemispherica_ Bull., _Cham. de Fr._, I., p. 93. 1829. _Didymium hemisphericum_ (Bull.) Fr., _Syst. Myc._, III., p. 115. 1829. _Diderma hemisphericum_ (Bull.) Horne., _Fl. Dan._, XI., p. 18. 1832. _Didymium michelii_ Lib., _Pl. Ard._, No. 180. 1873. _Chondrioderma michelii_ (Lib.) Rost., Fuckel, _Sym. Myc._, p. 74. Sporangia gregarious, orbicular, discoid, depressed above and often umbilicate below, stipitate or sometimes sessile, the outer peridium white, fragile, crustaceous, soon breaking about the margins, closely applied to the inner, which is delicate, cinereous, and ruptures irregularly; stipe about equal to the diameter of the sporangium, 1 mm., rather stout, calcareous but colored, brownish or alutaceous, more or less wrinkled longitudinally, the wrinkles when present forming veins on the lower surface of the sporangium; hypothallus small; columella not distinct from the thickened brownish or reddish base of the sporangium; capillitium of delicate threads, mostly simple and colorless, often scanty; spores pale violaceous, nearly smooth, 8-9 mu.