This well-marked species is certainly rare within our limits. We have specimens from New England and from Pennsylvania. The Iowa material referred to this species, _Bull. Lab. Nat. Hist. Ia._, II., p. 125, is _A. magna_ Rex. Rostafinski's figure is excellent in the present case, and gives the idea of what we regard the typical marking of the capillitium in _A. oerstedtii_. Externally the species resembles somewhat _A. nodulosa_, and the network of the capillitium is also suggestive of that form; the spiny capillitium is unique. Rare. Adirondacks, New York--_Dr. Rex._ 3. ARCYRIA NUTANS (_Bull._) _Grev._ PLATE II., Figs. 6, 6 _a_, 6 _b_. 1791. _Trichia nutans_ Bulliard, _Champ._, p. 122, t. 502, III. 1794. _Arcyria flava_ Pers., _Roemer N. Mag. Bot._, I., p. 90. 1824. _Arcyria nutans_ Grev., _Fl. Edin._, p. 455. Sporangia crowded, cylindric, about 2 mm. high when unexpanded, pale yellow or buff, short-stipitate or sessile by an acute base; peridium wholly evanescent, except at the base, where persists the shallow, colorless, often inwardly spinulose, plicatulate calyculus; stipe very short or wanting; hypothallus thin but usually in evidence; capillitium expanding to great length, forming an extremely flexile, plumose, pendulose open network of pale ochraceous tint, the threads 3-4 mu in thickness, adorned with spinules, sharp edged transverse plates sometimes rings, the surface especially marked by an indistinct reticulation; spore-mass buff or ochraceous, spores by transmitted light colorless, smooth or nearly so, 7-8 mu. This elegant species is not rare in undisturbed woods, especially on fallen willows. The expanded capillitia are very soft and plume-like, waving and nodding, very lightly attached below to the centre of the peridial cup. The capillitium threads are rough, with irregular spines and sharp-edged transverse plates, occasionally extending to form rings. Resembles the first species somewhat in habit, size, and the spinescent capillitium, but the resemblance is superficial only. The color is at once diagnostic, and the capillitium is after all entirely different. Not uncommon; Canada to Mexico; Maine to California; probably cosmopolitan. Bulliard's figure determines the synonymy. Persoon called the form _A. flava_, because Bulliard had missed the genus. 4. ARCYRIA VERSICOLOR _Phillips._ 1877. _Arcyria versicolor_ Phillips, _Grev._, V., p. 115. 1877. _Arcyria vitellina_ Phillips, _Grev._, V., p. 115.