1 86 THE NORTH AMERICAN SLIME-MOULDS 



4. PERICH^ENA MARGINATA Schweinitz. 



1831. PerichcEtia marginata Schw., N. A. F., No. 2310, p. 258. 



Sporangia depressed, globose, polygonal as they become 

 approximate or crowded, hoary canescent, sessile ; peridium 

 rather thick, persistent, circumscissile in dehiscence, covered 

 without by minute whitish calcareous (?) scales, within punctate 

 by the imprint of the spores ; hypothallus distinct, white ; capil- 

 litium scant or none ! Spores in mass dull yellow, by trans- 

 mitted light pale, nearly smooth, 14-15 p. 



Lister, following Rostafinski, includes this form with the 

 preceding. The differences between the two forms are, it 

 seems to us, sufficient to make convenient their separation 

 as by Schweinitz. Apart from the peculiar incrustation in 

 the present species, the larger spores, and especially the pecu- 

 liar white hypothallus, are distinctive. The method of dehis- 

 cence is also different. In P. corticalis the line of cleavage 

 before spore dispersal is indicated by a definite band surround- 

 ing the sporangium. Nothing similar appears in the gray 

 specimens of the present form, although the dehiscence is 

 quite as certainly circumscissile. The habitat in American 

 specimens is the outer surface of the bark, which causes the 

 species generally, by protective coloration, to be overlooked. 



Not common. Pennsylvania, Ohio, Missouri. 



C. 



Key to the Genera of the Arcyriese. 



A. Peridium becoming fragmentary, but persisting; capillitium non-elastic, 



i. LACHNOBOLUS 



B. Peridium evanescent above, persistent below ; capillitium elastic, 



2. ARCYRIA 



C. Capillitium elastic, bearing hamate branches, 3. HETEROTRICHIA 



i. Lachnobolus Fries. 



1829. Lachnobolus Fries, Syst. Myc., III., p. 177. 



