_b._ Sporangia elongate allantoid, etc., following No. 1. _Erionema_ =1. Fuligo= (_Haller_) _Pers._ 1753. _Mucor_ Linn., _Sp. Pl._ II., No. 1656 (?). 1768. _Fuligo_ Haller, _Hist. Helv._, Nos. 1233-1235, in part. 1801. _Fuligo_ Haller, _Pers. Syn._, p. 159. 1809. _Aethalium_ Link, _Diss._, I, p. 42. 1829. _Aethalium_ Fries, _Sym. Myc._, III., p. 92. Sporangia undefined, obscurely woven in and out among each other forming usually a cushion-shaped aethalioid mass. The outer layer sterile, often calcareous, forming a fragile crust, more or less defined. The middle layer sporiferous with calcigerous capillitium. The lowest layer a membranous hypothallus. The identity of this genus seems to have been recognized first by Haller, _op. cit._, but by Persoon more closely defined and illustrated. Link simply translated the name into Greek, for reasons less evident now, and in this was followed by Fries. Haller's designation is now probably securely fixed. The sporigerous median structure of the fructifications, under whatever specific name or names, is entirely confused. Sporangial walls, if ever such there were, are hardly as such recoverable, seemingly _indicated_ only, in the changes to which the aethalium submits as in the ripening the sporogenic plasm passes on to spores. In the present state of our knowledge the forms of this genus present withal a most perplexing problem. Are they simply phases of a single species, or are they in style and in structure sufficiently constant in their admitted variety, to claim specific rank and separate description? To follow the example of Greville and recognize in all the literature of two hundred years varied descriptions of a single type,--this were perhaps the easier and speedier disposal of the case. Fries thought so to treat the problem but was unable to keep faith with his own decision; for no sooner he states the genus monotypic than he proceeds forthwith to offer four varieties, a. b. c. d., viz. those by Persoon and others duly recognized as species. Recent students all, however, seem to find convenience in specific division. All seem disposed to honor Dr. Peck's _Fuligo ochracea_ whether or not by the name he gave; and of other varieties some seem impressed by the constancy of one, some of another characteristic, thus indicating that to careful observers all over the world there are differences that may be recognized, that have been recognized again and again. If there are two species there are certainly more. Out of the gatherings of many years one may set in order not less than five variations in the fruiting of _Fuligo_, five distinct types of fructification, to all appearing sufficiently constant for specific recognition.