28. PHYSARUM CONTEXTUM, Pers. Sporangia sessile and closely crowded together, roundish or more or less elongated, flexuous and complicate, the apex plane or impressed; the wall a firm yellowish membrane, covered by a thick pulveraceous layer of lime, white, ochraceous or yellow, easily crumbling and breaking up. Capillitium a loose net-work of tubules, much expanded at the angles; the nodules of lime very large, white or yellow, numerous, angular, and irregular, by confluence lobed and branched, sometimes massed together in the center of the sporangium. Spores globose, minutely warted, dark violaceous, 10-13 mic. in diameter. Growing on bark, leaves, mosses, etc. Sporangia with a width of .3-.5 mm. and varying in length from .5 mm. to 1 or 2 mm. The sporangia are often so much crowded as to appear to be grown together. _Diderma ochroleucum_ B. & C. belongs to this species. _Physarum conglomeratum_ Fr. is a closely related species, with smaller and smoother spores. I have not met with this. 29. PHYSARUM DIDERMA, Rost. Sporangia large, irregularly globose or oblong, sessile, but without a hypothallus, closely crowded together and sometimes confluent. The wall composed of two distinct and separate layers; the outer a thick, uneven, crustaceous, snow-white layer of lime; the inner a thin, violaceous membrane, cinereous from the adherent granules of lime, or free from them, and iridescent. Capillitium of tubules forming a loose net-work, with wide expansions at the angles; the nodules of lime numerous, snow-white, large, irregular, with pointed angles and lobes, sometimes confluent in the center of the sporangium. Spores globose, minutely warted, dark violaceous, 9-10 mic. in diameter. Growing on wood, bark, and mosses. Sporangia .8-1.0 mm. in diameter, more or less irregular. The wall of the sporangium is exactly like that of certain species of _Diderma_. This species must be rare, as I have met with it but twice in ten years, and I am not aware that it has ever been found by any one else. VIII. FULIGO, Haller. Aethalium a compound plasmodiocarp; the component sporangia branching and anastomosing in every direction, complicate and grown together; the walls of the sporangia a thin membrane, coated with minute, roundish granules of lime. Capillitium of tubules forming a net-work of irregular meshes, more or less expanded at the angles, the tubules containing in greater or less abundance irregular nodules of lime. Spores globose or sometimes ellipsoidal, violaceous. The genus is readily distinguished from _Spumaria_ by the round granules of lime upon the walls of the sporangia. §1. AETHALIUM, Link. Aethalia large; the lime in the capillitium scanty, the nodules small, ellipsoidal, or fusiform. _a. Aethalium with a thick fragile common cortex._