Growing on old leaves, wood, mosses, etc. Very common in this country. Sporangium .6-1.0 mm. in diameter, sometimes a little irregular, especially the form growing on mosses, and occasionally confluent. 9. DIDERMA CINEREUM, Morgan, n. sp. Sporangia subglobose, more or less irregular, somewhat depressed, sessile, usually close or crowded, sometimes confluent; the hypothallus a thin membrane, pellucid or with occasional patches of lime granules, sometimes not apparent. The wall very thin, even or rugulose, cinereous, the thin membrane covered by a single layer of closely-adherent granules of lime, rupturing irregularly. Columella white, hemispheric or depressed and irregular, the surface granulose. Capillitium of very slender, colored threads, the extremities pellucid, more or less branched. Spores globose, minutely warted, violaceous, 9-11 mic. in diameter. Plate XII, Fig. 46. Growing on old wood, leaves, etc. The sporangium .3-.5 mm. in diameter, thin and smooth or rugulose. The species superficially greatly resembles _Physarum cinereum_. 10. DIDERMA DIFFORME, Pers. Plasmodiocarp roundish, oblong, or more or less elongated and flexuous, scattered or seriately disposed; the hypothallus a thin brownish membrane, or commonly not apparent. The outer calcareous layer of the wall snow-white, thin, smooth, distinct from the inner membrane, breaking into pieces and falling away; the inner membrane thin, opaque and bluish or pellucid and iridescent. Columella reduced to a thin layer of scales and granules upon the brownish basal membrane. Capillitium scanty, consisting of short nearly colorless threads, which are simple, or fork a time or two. Spores globose, even, dark violaceous, 10-13 mic. in diameter. Growing on bark, leaves, twigs, herbaceous stems, etc. Plasmodiocarp .3-.5 mm. in thickness and variable in length, sometimes elongated several millimeters. 11. DIDERMA RETICULATUM, Rost. Plasmodiocarp very much depressed, roundish, oblong, much elongated and flexuous, closely crowded together and confluent; the hypothallus a thin white granulose layer of lime, scarcely broader than the plasmodiocarp. The outer calcareous layer of the wall white, distinct, very fragile and easily shelling off; the inner membrane much shrunken and withdrawn from the outer coat, rugulose, cinereous, with a dense closely-adherent layer of granules of lime. The columella a thin alutaceous, granulose-roughened layer, extending along the base of the plasmodiocarp. Capillitium of threads short and very slender, colorless, somewhat branched. Spores globose, even, pale violaceous, 6-8 mic. in diameter. Plate XII, Fig. 47. Growing on old wood, leaves, twigs, etc. Plasmodiocarp .5-.8 mm. in width, much flattened and usually closely crowded. The rough calcareous base of the plasmodiocarp might be considered as either all columella or all hypothallus, with the upper surface leather-colored. I am indebted to Arthur Lister, of London, for the determination of my specimens.