Sporangia gregarious, stipitate, globose snow-white, with a didymium like covering of calcareous particles; stipe white, not long, conical or tapering rapidly upward, slightly sulcate, brittle, from an evanescent hypothallus; columella none or small; capillitium, consisting of rather long hyaline threads, connecting the usual calcareous nodes, which are large, angular, snow-white; spore-mass black; spores by transmitted light, violet-brown, distinctly warted, about 10 mu. The snow-white, nearly smooth stem, the small sporangium (1/2 mm.) covered with loose calcareous granules, distinguish this rare species. It looks like a small _Didymium squamulosum_. Fries called it _D. leucopus_, _Syst. Myc._, III., p. 121. Rare. Iowa, Ohio, Maine; Portugal. 38. PHYSARUM COMPRESSUM _Alb. & Schw._ PLATE XVIII., Fig. 14, and PLATE XIX., Fig. 12 and Fig. 4. 1805. _Physarum compressum_ Alb. & Schw., _Fung. Lus._, p. 97. 1875. _Physarum nefroideum_ Rost., _Mon._, p. 93, in part. 1875. _Physarum affine_ Rost., _Mon._, p. 94. 1909. _Physarum compressum_ Alb. & Schw., Torrend, _Fl. des Myx._, p. 197. 1911. _Physarum compressum_ List., _Mycetozoa, 2nd ed._, p. 70. Sporangia more or less scattered, _compressed_-globose, or compressed-reniform, i. e. often umbilicate, stipitate, sessile, or elongate as if plasmodiocarpous, calcareous, white or ashen; peridium thin, covered with squamules, opening irregularly, usually by apical cleft; stipe, when present, short, stout, more or less sulcate, dark brown or ashen; capillitium a rather loose net, the nodules white, variable in size and shape; spores purplish-brown, delicately roughened, about 10-12.5 mu. _P. affine_ R. was in this connection set up for European types compressed indeed, but more strongly _reniform_. The author says in his further description that the form _affine_ is less definitely umbilicate, has white stems, etc.; allantoid, one would now say. Such forms now begin to appear in America; and if for these a specific name is needed, it is provided, _P. affine_ Rost., Plate XIX., Fig. 4. This seems to be a cosmopolitan species, now that we have found it. However, in North America it is rare. It is reported from Pennsylvania, from Colorado; Harkness found it in California, and the writer has often collected it in Oregon, on Mt. Rainier, Washington, and in California. Europe. 39. PHYSARUM NOTABILE _nom. nov._ PLATE IX., Figs. 2, 2 _a_, 2 _b_; PLATE XV., Fig. 2; and Frontispiece.