1. DIDYMIUM SQUAMULOSUM, A. & S. Sporangium variable in form and size, small and globose, or large and much depressed, the base usually umbilicate, stipitate, or sometimes sessile, and even plasmodiocarp; the wall very thin and pellucid, with a thin, gray-white layer of stellate crystals of lime, breaking up into subpersistent scales. Stipe short, erect, snow-white, longitudinally furrowed or plicate; the columella central, snow-white, various in shape, globose, obovoid, turbinate, and stipitate or sessile. Capillitium of numerous colorless threads, radiating from the columella and separating outwardly into several branches. Spores globose, very minutely warted, dark violaceous, 8-10 mic. in diameter. Growing on old wood, leaves, herbaceous stems, etc. Sporangium .4-.6-.8 mm. in diameter, the stipe scarcely longer than the diameter, often much shorter or nearly wanting. 2. DIDYMIUM PROXIMUM, B. & C. Sporangium globose or depressed-globose, the base more or less umbilicate, stipitate; the wall very thin and pellucid, with a loose white covering of stellate crystals of lime, the upper part breaking up and falling away. Stipe long, erect, tapering upward, yellow-brown to reddish-brown, expanding at the base into a small hypothallus; the columella central, white, turbinate, or discoid turbinate. Capillitium of slender, colorless threads, radiating from the columella, branching and often anastomosing. Spores globose, even, pale violaceous, 8-10 mic. in diameter. Plate XII, Fig. 37. Growing on old leaves, sticks, culms, etc. Sporangium .4-.6 mm. in diameter, the stipe two or three times the diameter. 3. DIDYMIUM EXIMIUM, Peck. Sporangium depressed-globose, the base umbilicate, sometimes very much depressed and also umbilicate above, stipitate; the wall pale ocher or pale yellow, with a thin layer of minute white crystals of lime, the upper part gradually breaking away. Stipe long, erect, tapering upward, pale yellow-brown, darker below, expanding into a small brown hypothallus; the columella central, large, discoid, or sometimes rough and irregular, pale ochre or yellowish. Capillitium of much-branched colorless threads, radiating upward and downward from the columella. Spores globose, very minutely warted, dark violaceous, 9-11 mic. in diameter. Plate XII, Fig. 38. Growing on old leaves, sticks, etc. Sporangium .5-.6 mm. in diameter, the stipe about twice the diameter. 4. DIDYMIUM MICROCARPUM, Fr. Sporangium small, globose, the base slightly umbilicate, stipitate; the wall a dark-colored membrane, covered with abundant snow-white crystals of lime. Stipe long, slender, erect, delicately striate, yellow-brown to blackish in color, expanded at the base into a small hypothallus; the columella small, globose, sessile or substipitate, pale yellow-brown. Capillitium of pale brown threads, somewhat branched and forming a loose net. Spores globose, very minutely warted, violaceous, 6-7 mic. in diameter.