Sporangia on the spines of fallen chestnut burs, scattered, pale yellow or whitish, small, globose, the peridium early evanescent above, more persistent below, stipitate; stipe small, tapering upward, from a small hypothallus; capillitium a dense but not expanding network attached chiefly to the lower portion of the sporangial wall, minutely waited or roughened, with few expansions or inflations; spores in mass pale yellow, under the lens colorless, almost smooth, 7-8 mu. This singular little species is remarkable chiefly in the habitat it affects,--fallen chestnut burs. On these almost universal, but on nothing else, except on the fallen catkins of the same species. Regarded by Mr. Lister as _A. cinerea_, from which it differs constantly in form, in capillitium more open and with larger threads, 4-5 mu in diameter as well as in its unique habitat, and yellowish color. Distribution coterminous with that of _Castanea dentata_ Borkhausen,--eastern half of the United States. 2. LACHNOBOLUS OCCIDENTALIS _Macbr._ PLATE II., Figs. 2, 2 _a_, 2 _b_; 4 and 4 _a_. 1885. _Lachnobolus incarnatus_ (Alb. & Schw.) Macbr., _Bull. Lab. Nat. Hist. Iowa_, II., p. 126. Sporangia scattered or crowded upon a hypothallus more or less distinct, globose or ellipsoidal, short-stipitate, varying somewhat in color, at first rosy or flesh-colored, later brownish or ochraceous; the peridium exceedingly thin, pellucid, mealy, evanescent above, persisting as a shallow cup below; capillitium inelastic, rather closely netted of threads variable in thickness, marked by frequent thickenings or expansions, everywhere warted, attached to the peridial walls, spores in mass flesh-colored, under the lens colorless, smooth, globose, 7.5-9 mu. This delicate and elegant little species appears to be not uncommon, but is probably generally passed over as an _Arcyria_, which it superficially resembles. When newly formed, the sporangia have a peculiar rosy or flesh-colored metallic tint, which is all their own. Within a short time this color passes, and most of the material comes from the field brownish or ochraceous in color. Typical sporangia are spherical on distinct short stipes; when crowded, the shape is of course less definite. The capillitium never expands as in _Arcyria_, but, exposed by the vanishing upper wall, remains a spherical mass resting upon the shallow cup-like base of the peridium.