1791. _Reticularia sinuosa_ Bulliard, _Champ._, p. 94; t. 446, Fig. 3. 1796. _Physarum bivalve_ Persoon, _Obs. Myc._, I., p. 6; t. III., Fig. 2. 1828. _Physarum sinuosum_ Wein., Fries _teste, l. c._ 1828. _Angioridium sinuosum_ Grev., _Scot. Crypt. Fl._, 310. 1829. _Physarum sinuosum_ Fries, _Syst. Myc._, III., p. 145. 1875. _Physarum sinuosum_ (Bull.) Rost., _Monograph_, p. 112. 1892. _Physarum sinuosum_ Rost., Massee, _Mon._, p. 305. 1894. _Physarum bivalve_ Pers., Lister, _Mycetozoa_, p. 57. 1896. _Angioridium sinuosum_ (Grev.), Morg., _Cin. Soc. Nat. Hist._, p. 75. 1899. _Physarum sinuosum_ (Bull.) Wein., Macbr., _N. A. S._, p. 28. 1911. _Physarum sinuosum_ Wein., Lister, _Mycetozoa, 2nd ed._, p. 76. Sporangia distinct or plasmodiocarpous, the plasmodiocarp creeping in long vein-like reticulations or curves, laterally compressed; sometimes distinct and crowded, always sessile. Peridium double; the outer thick, calcareous, fragile, snow-white; the inner delicate, the dehiscence by more or less regular longitudinal fissure. Capillitium strongly developed with abundant white, calcareous granules. Spores smooth, dull violet, 8-9 mu. Plasmodium pale gray, or nearly white. Easily recognized at sight by its peculiar form, bilabiate and sinuous. Apart from microscopic structure, perfectly described by Fries, _Syst. Myc._, p. 145. Bulliard called it _Reticularia sinuosa_. Habitat various, but not infrequently the upper surface of the leaves of living plants, a few inches from the ground. The two sorts of fructification often occur side by side, or merge into one another from the same plasmodium. Where the substratum affords room the plasmodiocarpous style prevails; in narrower limits single sporangia stand. The calcareous deposit on the peridium is usually very rich and under a lens appears made up of countless snowy or creamy flakes. Forms occur, however, in which these outer calcic deposits are almost entirely wanting; the peridium becomes transparent, the capillitium visible from without. Judging from material before us, this appears to be the common presentation in western Europe. See also No. 5 following. Widely distributed. New England to the Carolinas, and Louisiana west to South Dakota and Nebraska, Iowa and Washington. 5. PHYSARUM BITECTUM _List._ PLATE XIX., Fig. 16. 1891. _Physarum diderma_ Rost., List., _Jour. Bot._, XXIX., p. 260. 1894. _Physarum diderma_ Rost., List., _Mycetozoa_, p. 57. 1911. _Physarum bitectum_ List., _Mycetozoa, 2nd ed._, p. 78.