_B._ Outer sporangial wall cartilaginous, the inner less distinct, or concrete with the outer; species oftener stipitate _Leangium_ _A._ Sub-Genus DIDERMA 1. Fructification wholly plasmodiocarpous 1. _D. effusum_ 2. Fructification of distinct sporangia. _a._ Sporangia on a common hypothallus. O Outer wall fragile, not widely remote from the inner 2. _D. spumarioides_ OO Inner wall lacking 3. _D. simplex_ OOO Outer wall crustaceous, porcelain-like. i. Spores 8-10 4. _D. globosum_ ii. Spores 12-15 5. _D. crustaceum_ OOOO Outer wall firm, not crustaceous 6. _D. lyallii_ _b._ Sporangia isolated, or, at least, not on a common hypothallus, sessile. O Outer wall porcellanous, roseate 7. _D. testaceum_ OO Outer wall white 8. _D. niveum_ OOO Outer wall ashen 9. _D. cinereum_ _c._ Sporangia stipitate 10. _D. hemisphericum_ _B._ Sub-Genus LEANGIUM 1. Sporangia generally sessile. _a._ Inner peridium distinct. O Membranous colorless, columella scant 11. _D. sauteri_ OO Colorless, columella prominent, red 12. _D. cor-rubrum_ OOO Outer ochraceous, inner yellow 13. _D. ochraceum_ _b._ Peridial layers inseparable. O Peridium multifid; columella small or none 16. _D. trevelyani_ OO Peridium breaking into but few irregular lobes; columella prominent. i. Peridium umber brown 14. _D. roanense_ ii. Peridium ashen 15. _D. radiatum_ iii. Peridium chocolate without, inside white 17. _D. asteroides_ 2. Sporangia stipitate. _a._ Peridium pallid, smooth 18. _D. floriforme_ _b._ Peridium white, rugulose 19. _D. rugosum_ 1. DIDERMA EFFUSUM (_Schw._) _Morgan._ 1831. _Physarum effusum_ Schw., _N. A. F._, p. 257. 1896. _Diderma effusum_ (Schw.) Morg., _Jour. Cin. Soc._, p. 71. 1899. _Diderma effusum_ (Schw.) Morg., Macbr., _N. A. S._, p. 94. 1899. _Diderma reticulatum_ Rost., Macbr., _N. A. S._, p. 95. 1911. _Diderma effusum_ Morg., Lister, _Mycetozoa, 2nd ed._, p. 102.