Sporangia sessile, or short stipitate; peridial wall double, the outer thick, destitute of lime, polished, shining within and without, the inner very delicate, enclosing the capillitium and spores; capillitium of two, more or less, distinct systems, the one a delicate network of hyaline, limeless threads, the other calcareous throughout, or nearly so, the meshes large and the threads or tubules broad; columella none, although a pseudo-columella may sometimes be detected. This genus was by Link established on characters purely external. Rostafinski supplemented Link's definition by calling attention to the peculiar character of the capillitium and to microscopic characters in general. The outer peridium is thick and strong, unlike the ordinary structure in _Physarum_. Some physarums, however, have a very similar outer wall; _P. brunneolum_, for instance; compare the peridium of _P. citrinellum_. In dehiscence and structure there is also some resemblance to some species of _Diderma_, and by Persoon and Fries the common species was so referred, but the capillitium is again definitive. A critical study of all these things really begins with Rostafinski's microscope. Under his definition of the present genus _P. squamulosum_ Wingate and _P. albescens_ Ell. might well be entered here. Such course at present would but increase confusion, and until by future research the ontogeny of all these, and so their relationship, shall be more exactly known, the genus may be left with its historic species,--montotypic. LEOCARPUS FRAGILIS (_Dickson_) _Rost._ PLATE VIII., Figs. 3, 3 _a_, 3 _b_. 1785. _Lycoperdon fragile_ Dickson, _Fasc. Pl. Crypt. Brit._, I., p. 25. 1795. _Diderma vernicosum_ Persoon, _Ust. Ann. Bot._, XV., p. 34. 1809. _Leocarpus vernicosum_ Link, _Diss._, I., p. 25. 1875. _Leocarpus fragilis_ (Dicks.) Rost., _Mon._, p. 132. Sporangia gregarious or clustered, sessile or stipitate, obovoid, rusty or spadiceous-yellow, shining; peridium opening at maturity in somewhat stellate fashion; stipe filiform, white or yellow, weak and short; spores dull black, spinulose, 12-14 mu. A common species, distributed through all the world, Iowa to Tasmania. Recognizable at sight by the form and color of the sporangia. In shape and posture these resemble the eggs of certain insects, and, occurring upon dead leaves, generally where these have drifted against a rotten log, they might perchance be mistaken for such structures. With no other slime-moulds are they likely to be confused. The outer peridium opens irregularly, or more rarely stellately. At centre of the capillitium is a calcareous core. The plasmodium is yellowish white, spread in rich and beautiful reticulations. _N. A. F._, 1123.