Plasmodiocarp bent or short-flexuous, often arcuate or completely annular, dark chestnut brown or black, opening irregularly; peridium thin, brittle, translucent, covered without by a rather dense layer of brownish or black brown scales; capillitium of long, sparingly branched threads furnished with projecting spinules remarkable for their length, about twice the diameter of the thread; spores yellow, minutely but distinctly warted, about 12 mu. This is the common species everywhere on the inner side of the bark of fallen trees, _Ulmus_, etc. It is readily distinguished at sight by the peculiar annular, looped, and U-shaped plasmodiocarps, with their dark umbrine or blackened surface. From the preceding it is especially distinguished by the spinulose capillitium and larger spores. Not rare. New England, New York, Pennsylvania, Ohio. =2. Perichaena= _Fries_ 1817. _Perichaena_ Fries, _Symb. Gast._, p. 11. Sporangia flattened, sometimes small and roundish, more often larger, polygonal by mutual interference, or irregular, the peridium thickened outwardly by a dense reddish or brownish layer of scales; dehiscing by circumscission or by a lid; capillitium often scant, of slender, warted, yellowish threads, attached betimes to the upper wall; spores yellow, oval or spherical. =Key to the Species of Perichaena= _A._ Sporangia plainly flattened. _a._ Very flat, sporangia 1mm. or more in width 1. _P. depressa_ _b._ Depressed; sporangia smaller 2. _P. quadrata_ _B._ Sporangia more or less spherical _a._ Chestnut brown 3. _P. corticalis_ _b._ Gray or canescent 4. _P. marginata_ 1. PERICHAENA DEPRESSA _Libert._ PLATE XVII., Fig. 10. 1837. _Perichaena depressa_ Lib., _Fl. Crypt. Ard._, IV., No., 378. Sporangia sessile, applanate, crowded, polygonal by mutual contact, fuscous or chestnut brown, shining, opening by a definite lid; spore-mass and capillitium yellow, the capillitium well developed, of slender yellow threads of various widths, almost smooth; spores minutely warted, 10-12 mu. Easily recognized by the peculiar, polygonal, depressed-flattened sporangia and consequent shallow spore-cases in which lie the yellow spores and scanty capillitium. Rostafinski refers here _P. vaporaria_ Schw., No. 2311, but the meagre description seems rather to apply to the next species. The original material is no longer accessible. In the crevices and on the inside of bark of fallen logs of various sorts, walnut, maple, etc. Not commonly collected. Specimens are before us from New England, Illinois, Iowa, Missouri, Florida, Mexico, Nicaragua. Probably over the whole wooded region of the continent. 2. PERICHAENA QUADRATA _Macbr._ 1893. _Perichaena irregularis_ Berk. & C., Morgan, _Jour. Cin. Soc._, p. 20.