3. FULIGO FLAVA, Pers. Plasmodium effused lemon-yellow. Aethalium mostly effused, irregular, the surface reticulate, pitted and perforate, entirely naked, pale yellow to lemon-yellow and greenish-yellow, the hypothallus thin or scarcely evident. Sporangia laterally much compressed, flexuous, and gyrose, not everywhere grown together, but forming a dense reticulum; the walls a thin, pellucid membrane, with a dense layer of lemon-yellow granules of lime. Capillitium of short and very slender tubules, sparingly branched and scarcely forming a net-work, not expanded at the angles; the tubules very scantily furnished with lime, in scattered, small, fusiform nodules, white or lemon-yellow. Spores globose, very minutely warted, violaceous, 7-9 mic. in diameter. Growing on mosses, old leaves, sticks, etc.; not common. Aethalia in irregular patches 2-4 cm. or more in extent, sometimes almost reduced to a simple plasmodiocarp. This species furnishes a clear notion of the structure of the aethalium in the other species, on account of the sporangia being but loosely compacted and not entirely grown together. The _Fuligo vaporaria_ Pers., of the green-houses and gardens I have never seen; the _Mucor septicus_ Linn., was thought to be the plasmodium of this. Linnæus's description is simply "_Mucor unctuosus flavus._" §2. AETHALIOPSIS, Zopf. Aethalium small; lime abundant in the capillitium, the nodules numerous and large, angular and irregular. 4. FULIGO MUSCORUM, A. & S. Plasmodium effused, golden yellow. Aethalium small, subpulvinate, irregular, the surface furnished with scattered, irregular scales of lime, whitish or ochraceous to golden yellow in color, arising from a thin, white, membranaceous hypothallus. Sporangia closely packed and grown together; the walls a thin, violaceous membrane, rugulose, with a thin, closely adherent layer of granules of lime. Capillitium a loose net-work of tubules, widely expanded at the angles; the tubules for the most part filled with lime, the nodules white or yellowish, numerous, very large, angular and irregular, sometimes confluent with pointed lobes and branchlets. Spores irregularly globose, minutely warted, dark violaceous, 9-11 mic. in diameter. Growing on leaves, twigs, mosses, etc. Aethalium from 2 or 3 mm. to a centimeter or more in extent. I have a specimen of _Fuligo simulans_ Karsten, from Karsten himself; it is identical with my specimens of _Fuligo ochracea_ Peck. There could be no better representation of these specimens made at that time than the description and figure of _Fuligo muscorum_ A. & S., in the _Conspectus_.