Aethalium depressed, flat; the sporangia erect, regular, prismatic by mutual pressure, the peridia convex above, wanting at the sides and within the aethalium represented by vertical threads marking the angles and passing from base to summit. This genus is readily recognized by the internal structure of the aethalium. The lateral wall-openings, which, as we have seen, characterize the sporangia of the preceding genus, here become extreme, occupying to such extent the lateral wall-space of each sporangium that only threads remain to mark the vertical angles. In 1873 Rostafinski applied the generic name here adopted, because he thought he discovered close relationships with _Dictydium_. In 1875, believing his first impressions erroneous, and desirous that the nomenclature might not at once mislead the student and perpetuate the memory of his own mistake, the same author proposed the name by which the genus has generally ever since been known--_Clathroptychium_. However sensible the latter conclusion reached by our Polish author, it is plainly contrary to all rules of priority. Our region shows but a single widely distributed species,-- 1. DICTYDIAETHALIUM PLUMBEUM (_Schum._) _Rost._ PLATE I., Figs. 2, 2 _a_, 2 _b_. 1803. _Fuligo plumbea_ Schum., _Enum. Saell._, No. 1410. 1833. _Licea rugulosa_ Wall., _Cr. Fl. Ger._, IV., p. 345. 1873. _Dictydiaethalium plumbeum_ (Schum.) Rost., _Versuch_, p. 5. 1875. _Clathroptychium rugulosum_ (Wallr.) Rost., _Mon._, p. 225. 1894. _Dictydiaethalium plumbeum_ Rost., List., _Mycetozoa_, p. 157. Aethalium thin, very flat, olivaceous or ochraceous, smooth, under the lens punctate, in section showing the columnar or prismatic sporangia, which are normally six-sided, having at the edges six simple threads, the remains of peridium, extending from base to apex, where the peridium remains intact, arcuate; hypothallus prominent, radiating far around the aethalium, silvery white; spores in mass, ochraceous, or dull brownish yellow, by transmitted light almost colorless, rough 9-10 mu. Not rare, on decaying logs, especially of _Tilla americana_, where in the same place successive fructifications follow each other sometimes for weeks together in the latter part of summer and early fall. The aethalium is generally elliptical or elongate, 2-3 cm. in extent, sometimes irregular or branched, varying in color according to degree of maturity, weathering, etc. Plasmodium at first watery, then pink, or flesh-colored. Eastern United States; common. Toronto;--_Miss Currie._ _E._ CRIBRARIACEAE Sporangia distinct, more or less closely gregarious, stipitate, the peridium opening, especially above, by a well-defined network formed from thickenings in the original sporangial wall. =Key to the Genera of the Cribrariaceae= _A._ Peridial thickenings in form of an apical net with definite thickenings at the intersections of the component threads 1. CRIBRARIA