Sporangia cylindric or globose, stipitate; stipe prolonged upward to form a more or less extended and tapering columella bearing branches on every side, which by repeated divisions and reunions form the capillitium; ultimate branch-tips free, not supporting a surface net parallel to the peridial wall; peridium evanescent, perhaps sometimes not developed at all. The genus _Comatricha_ was set off from _Stemonitis_ by the joint effort of Preuss (1851) and Rostafinski (1873-5). Preuss included in his genus, _Comatricha_, alien forms, and besides failed to give an accurate definition; included, however, in his list some species which have since been known by his generic name. The distinction between the two genera is almost an artificial one, and species are sometimes arbitrarily assigned to one genus or the other. The diagnosis in any case turns upon the presence or absence of a surface net, formed, in _Stemonitis_, by the anastomosing of the ultimate divisions of the capillitial branches. In _Comatricha_ the anastomosing is general, from the columella out, and is not specialized at the surface. Recent attempts to reunite the genera here compared seem to result in no apparent advantage. The genera come very near together, but their separation along the line suggested by Rostafinski remains convenient. =Key to the Species of Comatricha= _A._ Sporangia closely clustered. _a._ Obovate or short cylindric. 1. Spores verruculose 1. _C. caespitosa_ 2. Spores reticulate 2. _C. cylindrica_ _b._ Elongate, reddish-brown, tufts extended 3. _C. flaccida_ _B._ Sporangia scattered more or less widely. _a._ Capillitium lax, open. i. Sporangia long, 10-12 mm. 4. _C. longa_ ii. Sporangia shorter, capillitium irregular 5. _C. irregularis_ _b._ Capillitium dense. i. Sporangia large, to 10 mm., spore-mass black 7. _C. suksdorfii_ ii. Sporangia smaller--6 mm. O Spore-mass brown, spherical, conoidal, etc., generally with more or less lengthened stipe 8. _C. nigra_ OO Spore-mass violaceous or purplish 9. _C. aequalis_ iii. Sporangia ovate or cylindric, minute, to 3.5 mm. O Cylindric, spore with few, scattered warts 10. _C. typhoides_ OO Smaller, capillitium irregular, loose 6. _C. laxa_ OOO Total height to 2 mm. or much less. + Columella digitately divided 11. _C. elegans_ ++ Columella lamprodermoid, and on leaves 12. _C. rubens_