94 THE NORTH AMERICAN SLIME-MOULDS 



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



sessile. 

 * Outer wall porcellanous, roseate . . . 8. D. testaceum 



** Outer wall white 9. D. niveum 



*** Outer wall ashen 10. D. cinereum 



c. Sporangia stipitate n. D. hemisphericum 



B. SUB-GENUS LEANGIUM. 



1. Sporangia generally sessile. 



a. Inner peridium distinct 13. D. sauteri 



b. Peridial layers inseparable. 



* Peridium multifid ; columella small or none, 12. D.trevelyani 

 ** Peridium breaking into but few irregular lobes ; columella 



prominent. 



i. Peridium umber brown . . .14. D. roanense 

 ii. Peridium ashen 15. D. stellar e 



2. Sporangia stipitate. 



a. Peridium pallid, smooth . . . . . 17. D.floriforme 



b. Peridium white, rugulose 1 6. D. rugosum 



I. DIDERMA EFFUSUM (Sc/izv.) Morgan. 



1831. Physarujn effitsnm Schw., N. A. F., p. 257. 



1896. Diderma effusuin (Schw.) Morg., /<?;-. Cm. Soc., p. 71. 



Fructification plasmodiocarpous, reticulate, creeping, appla- 

 nate and generally widely effused, white ; the peridium thin, 

 cinereous, covered by a delicate, white, calcareous crust ; the 

 columella simply the base of the plasmodiocarp, thin aluta- 

 ceous ; the capillitium pale, consisting of short threads some- 

 what branched toward their distal extremities ; spores smooth, 

 pale violaceous, 8-10 /*. 



This is PJiysarnni cffnsnm Schw., v. N. A. F., No. 2297. It is 

 reported by Morgan from Ohio, and we have one specimen 

 from eastern Nebraska, so that it is probably of general dis- 

 tribution in the eastern United States. It might be taken 

 for an exceptionally plasmodic form of the next species, 

 but is distinguished by the extreme thinness of the fructifica- 

 tion and its pure white color ; it looks like a splash of 



'$ 



whitewash. 



