1873. _Didymium connatum_ Peck, _Rep. N. Y. Mus._, XXVI., p. 74. 1879. _Physarum polymorphum_ (Mont.) Rost., Peck, _Rep. N. Y. Mus._, XXXI., p. 55. 1893. _Physarum leucophaeum_ Fr., Ellis, _N. A. F._, No. 2396, _second exhibit_. 1893. _Physarum leucophaeum_ Fries, Macbr., _Bull. Lab. Nat. Hist. Iowa_, II., p. 156. 1894. _Physarum compressum_ Alb. & Schw., List., _Mycetozoa_, p. 53, in part. 1896. _Physarum connexum_ Link., Morg., _Jour. Cin. Soc._, p. 92, in part. 1896. _Physarum confluens_ Pers., Morg., _l. c._, p. 94. 1899. _Physarum nefroideum_ Rost., Macbr., _N. A. S._, p. 41, in part. 1911. _Physarum connatum_ Lister, _Mycetozoa, 2nd ed._, p. 71. Sporangia gregarious, sessile, stipitate, or even plasmodiocarpous; when stipitate, depressed, varying at times to irregular reniform in the same colony; globose, the peridium strongly calcareous, cinereous-white; stipe variable, generally tapering upward, always distinctly deeply plicate-furrowed throughout, in color dark, opaque, sometimes touched with white or gray; capillitium abundant, the white lime-knots, varying in size and shape, connected by rather long hyaline threads, with here and there an empty node; spore-mass black, by transmitted light, dark, sooty brown, minutely papillose, 10-11.5 mu. This remarkable species, while not at all difficult of recognition to one familiar with its phases, is withal very difficult to define. Normally stipitate, it often shows from the same plasmodium all sorts of forms, the shape of the fructification dependent apparently upon external conditions prevalent at the time. The amount of calcium also varies, especially in the capillitium, where there is usually much, with a tendency to the formation of something like a pseudo-columella; the outer net in such cases nearly destitute. The calcium in the stipe also varies; the black or brown stipes are, of course, free from it; the gray or white, calcareous. In this large and difficult genus, since spore-color is receiving increased consideration,--see No. 31 preceding,--it is proper to note that in the present case two types appear, one with spore-color under the lens, as described, the other with spores violaceous with no trace of black; unshadowed.