130 THE NORTH AMERICAN SLIME-MOULDS 



A. Sub-Genus DIDERMA 



1. Fructification wholly plasmodiocarpous . . . \. D. effusum 



2. Fructification of distinct sporangia. 



a. Sporangia on a common hypothallus. 



* Outer wall fragile, not widely remote from the inner 



2. D. spumarioides 

 ** Inner wall lacking . . . . 3. D, simplex 

 *** Outer wall crustaceous, porcelain-like. 



i. Spores 8-10 . . . 4-. D. globosum 



ii. Spores 12-15 . . . 5. D. crustaceum 



**** Outer wall firm, not crustaceous . 6. D. lyallii 



b. Sporangia isolated, or, at least, not on a common hypothallus, 



sessile. 



* Outer wall porcellanous, roseate . 7. D. testaceum 

 ** Outer wall white . . . . 7. D. niveum 



*** Outer wall ashen . . . . 9. D. cinereum 

 . c. Sporangia stipitate . , . . 10. D. hemispherkum 



B. Sub-Genus LEANGIUM 



1. Sporangia generally sessile. 



a. Inner peridium distinct. 



* Membranous colorless, columella scant 11. D. sauteri 

 ** Colorless, columella prominent, red 12. D. cor-rubrum 



*** Outer ochraceous, inner yellow . 13. D. ochraceum 



b. Peridial layers inseparable. 



* Peridium multifid; columella small or none 



16. D. trevelyani 

 ** Peridium breaking into but few irregular lobes; colum- 

 ella prominent, 

 i. Peridium umber brown . 14. D. roanense 

 ii. Peridium ashen . . . 15. D. radiatum 

 iii. Peridium chocolate without, inside white 



17. D. aster aides 



2. Sporangia stipitate. 



a. Peridium pallid, smooth . . . . 18. D. floriforme 



b. Peridium white, rugulose . . . . 19. D. rugosum 



1. DiDERMA EFFUSUM (Schiv.) Morgan. 



1831. Physarum effusum Schw., A''. A. F., p. 257. 



1896. Diderma effusum (Schw.) Morg., Jour. Cin. Soc, p. 71. 



1899. Diderma effusum (Schw.) Morg., Macbr., A^. A. S., p. 94. 



1899. Diderma reticulatum Rost., Macbr., N. A. S., p. 95. 



1911. Diderma effusum Morg., Lister, Mycetozoa, 2nd ed., p. 102. 



Fructification plasmodiocarpous, reticulate, creeping, applanate and 

 generally widely effused, white ; the peridium thin, cinereous, covered 



