_A._ DIANEMACEAE =Key to the Genera of the Dianemaceae= _A._ Capillitial threads attached at one end, or free 1. MARGARITA _B._ Capillitial threads attached at each end 2. DIANEMA =1. Margarita= _List._ 1894. _Margarita_ Lister, _Mycet._, p. 203. Sporangia sessile, the capillitium simple, hair-like, coiled. 1. MARGARITA METALLICA (_Berk. & Br._) _List._ PLATE XVII., Figs. 1, 1 _a_, 1 _b_. 1838. _Physarum metallicum_ Berk. & Br., _Mag. Zool. & Bot._, I., p. 49. Sporangia scattered or clustered, globose, or somewhat plasmodiocarpous, .5-1 mm., sessile, coppery iridescent, the peridium thin, opening above irregularly; capillitium of long flexuous, coiling, simple or little dividing threads, nearly smooth, with infrequent attachments to the peridial wall; spores in mass yellowish, transparent under the lens, delicately verruculose, 10-12 mu. One of the handsomer species of the present group. So far a Pacific coast form. California, Oregon, Washington; reported from Chile. =Dianema= _Rex_ 1891. _Dianema harveyi_ Rex, _Proc. Phil. Acad._, p. 397. Sporangia simple or plasmodiocarpous; capillitium composed of threads without characteristic thickenings running entirely across the sporangium attached both to the base and to the opposite wall, not joined to form a network. =Key to Species of Dianema= _A._ Sporangia distinct, iridescent 1. _D. harveyi_ _B._ Fructification more or less plasmodiocarpous, dull brown 2. _D. corticatum_ _C._ Sporangia, some of them stipitate 3. _D. andersoni_ 1. DIANEMA HARVEYI _Rex._ PLATE XVI., Figs. 5 and 5 _b_. 1891. _Dianema harveyi_ Rex, _Proc. Phil. Acad._, p. 397. Sporangia gregarious, generally rounded or cushion-shaped, depressed, sessile, iridescent bronze, 1 mm. in diameter; peridium thin, translucent, opening irregularly; capillitium of simple threads, not netted, but often forked two or three times, taut, running from base to top; spores yellow, by transmitted light pale yellowish, minutely roughened, 8-10 mu. This interesting species was collected in Orono, Maine, in 1889, by Professor F. L. Harvey, and so far as can be learned has not been taken since. Mr. Lister records two species from England which he refers to this genus. As to its systematic place, Dr. Rex says, _l. c._ "It stands as a single representative of a new and separate family adjoining the _Perichaenacae_ in the order _Calonemeae_ of Rostafinski." Rare. Maine. 2. DIANEMA CORTICATUM _List._ PLATE XVI., Figs. 5 _a_, 5 _c_. 1894. _Dianema corticatum_ List., _Mycetozoa_, p. 205.