1831. _Perichaena marginata_ Schw., _N. A. F._, No. 2319, p. 258. Sporangia depressed, globose, polygonal as they become approximate or crowded, hoary canescent, sessile; peridium rather thick, persistent, circumscissile in dehiscence, covered without by minute whitish calcareous (?) scales, within punctate by the imprint of the spores; hypothallus distinct, white; capillitium scant or none! Spores in mass dull yellow, by transmitted light pale, nearly smooth, 14-15 mu. Lister, following Rostafinski, includes this form with the preceding. The differences between the two forms are, it seems to us, sufficient to make convenient their separation as by Schweinitz. Apart from the peculiar incrustation in the present species, the larger spores, and especially the peculiar white hypothallus, are distinctive. The method of dehiscence is also different. In _P. corticalis_ the line of cleavage before spore dispersal is indicated by a definite band surrounding the sporangium. Nothing similar appears in the gray specimens of the present form, although the dehiscence is quite as certainly circumscissile. The habitat in American specimens is the _outer_ surface of the bark, which causes the species generally, by protective coloration, to be overlooked. Not common. Pennsylvania, Ohio, Missouri. _C._ ARCYRIACEAE =Key to the Genera of the Arcyriaceae= _A._ Peridium becoming fragmentary, but persisting; capillitium non-elastic 1. LACHNOBOLUS _B._ Peridium evanescent above, persistent below; capillitium elastic 2. ARCYRIA _C._ Capillitium elastic, bearing hamate branches 3. HETEROTRICHIA =1. Lachnobolus= _Fries_. 1829. _Lachnobolus_ Fries, _Syst. Myc._, III., p. 177. Sporangia distinct, sessile or nearly so, globose or cylindric, often distorted, scattered or densely crowded, the peridium extremely thin, ruptured irregularly, and persistent in fragments; capillitium attached at numerous points to the sporangial wall, forming a dense net, the threads warted or spinulose, non-elastic. Species of this genus are easily distinguished from those of the next by the peculiar fragile peridium and the inelastic capillitium. =Key to the Species of Lachnobolus= _A._ Sporangia pale yellow, on fallen flowers and fruit-burs of Castanea 1. _L. globosus_ _B._ Sporangia rosy or copper-colored, at length ochraceous 2. _L. occidentalis_ 1. LACHNOBOLUS GLOBOSUS (_Schw._) _Rost._ 1822. _Arcyria globosa_ Schw., _Syn. Fung. Carol._, No. 400. 1875. Lachnobolus globosus (Schw.) _Rost., Mon._, p. 283. 1894. _Arcyria albida_ Pers. (in part) Lister, _Mycetozoa_, p. 186.