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.
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 µ.
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.
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.
1. Fructification æthalioid 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_