126 THE NORTH AMERICAN SLIME-MOULDS 



on the hemisphere and other minute but variable markings; 9-10 fi. 

 Seattle, Washington. 



Differs from D. nigripes in color of the stipes, capillitium, spore- 

 diameter, etc. 



15. DiDYMIUM DUBIUM Rost. 



1875. Didymium dubium Rost., Mon., p. 152. 



1892. Didymium listeri Mass., Mon., p. 244. 



1894. Didymium dubium Rost., List, Mycetozoa, p. 95. 



1911. Didymium dubium Rost., List., Mycetozoa, 2nd ed., p. 126. 



Fructification wholly plasmodiocarpous, snow-white, small, 2-6 

 mm., flat and thin; the outer wall double, membranous within, cal- 

 careous-crystalline without; columella none; capillitium simple of 

 rather thick, vertical, brown threads, sparingly united laterally, and 

 only occasionally furcate at the ends, especially above ; spores minutely 

 spinulescent, violaceous pale, 12-15 /x. 



Massee thought English specimens out of harmony with the orig- 

 inal description and gave them a new name. To refuse this, Lister 

 enlarges the range of spore-measurements and disregards some of 

 Rostafinski's specifications as to capillitium. Our specimens are as 

 described. 



Bohemia. England. Shores of Lake Okoboji, Iowa. 



This is indeed a doubtful form. It differs from D. difforme 

 chiefly in that the outer calcareous shell is not smooth, but is covered 

 with abundant loose crystals, frosted. The spores are paler but about 

 the same size. The frosting may be incident to local climatic condi- 

 tions at the time and place of desiccation. 



16. Didymium difforme Duby. 



1797. Diderma difforme Pers. Tentamen Disp. Meth., p. 19. 



1830. Didymium difforme Duby., Bat. Gall, ii., p. 858. 



1875. Chondrioderrna difforme Pers., Rost., Mon., p. 177. 



1894. Didymium difforme Duby., List., Mycetozoa, p. 94. 



1899. Diderma personii Macbr., A^. A. S., p. 96. 



1911. Didymium difforme Duby., List., Mycetozoa, 2nd ed., p. 124, 



Plasmodiocarpous, the smooth, white outer peridium separable from 

 the thin, colorless or purplish inner layer; capillitium of rather 



