A plasmodiform gathering of this species which will be mistaken for an entirely different thing, is yellow, sessile, and has _adherent_ spores; looks like a badhamia, but is after all a leocarpus and probably belongs here. The spores are irregularly clustered and the badhamioid section of the capillitium seems now dominant. California. B. DIDYMIACEAE =Key to the Genera of the Didymiaceae= 1. Fructification aethalioid 1. _Mucilago_ 2. Fructification plasmodiocarpous, or forming more often distinct sporangia. _a._ Calcareous deposits crystalline, stellate 2. _Didymium_ _b._ Calcareous deposits amorphous, peridium double 3. _Diderma_ _c._ Calcareous deposits in form of scattered scales 4. _Lepidoderma_ _d._ Peridium double, the outer gelatinous 5. _Colloderma_ =1. Mucilago= (_Mich._) _Adans._ 1729. _Mucilago_ Micheli, _Nov. Pl. Gen._, in part. 1763. _Mucilago_ (Mich.) Adanson, _Fam. des Pl._, II., p. 7. 1791. _Spumaria_ Pers. in Gmelin, _Syst. Nat._, II., p. 1466. Fructification aethalioid, consisting generally of large cushion-shaped masses covered without by a white foam-like crust; within, composed of numerous tubular sporangia, developed from a common hypothallus, irregularly branched, contorted and more or less confluent; the peridial wall thin, delicate, frosted with stellate lime-crystals, which mark in section the boundaries of the several sporangia; capillitium of delicate threads, generally only slightly branched, terminating in the sporangial wall, marked with occasional swellings or thickenings. By the descriptions offered by most authors, and especially by Rostafinski's figures (_Mon._, Pl. ix.), a pronounced columella is called for in the structure of _Spumaria_. The individual sporangia rise from a common hypothallus, and occasionally portions of this run up and give to a sporangium the appearance of being stipitate. Sometimes also this upper extension of the hypothalline protoplasm passes beyond or behind the base of the sporangium or between two or more, and is more or less embraced by these in their confluent flexures. This, it seems, suggested Rostafinski's elaborate diagram, Fig. 158; at least, none other form of columella is shown by American materials at hand. 1. MUCILAGO SPONGIOSA (_Leyss._) _Morgan._ PLATE VII, Figs. 6, 6 _a_, 6 _b_. 1783. _Mucor spongiosus_ Leysser, _Fl. Hal._, p. 305. 1791. _Reticularia alba_ Bull., _C. Fl. France_, p. 92. 1791. _Spumaria mucilago_ Pers., Gmel., _Syst. Nat._, II., 1466. 1805. _Spumaria alba_ (Bull.) DC., _Fl. Fr._, II., p. 261. 1897. _Mucilago spongiosa_ (Leyss.) Morg., _Bot. Gaz._, XXIV., p. 56.