Genera and species. 131 



what areolate, grayish in color, partially enclosing the 

 apothecia. Apothecia comparatively large, irregular 

 in outline. Disk dark. Spores not seen. 



10. Arthonia atra. Thallus rudimentary, mostly 

 hypophl(]eodal, light color. Apothecia numerous, 

 oblong to linear or branching. Disk dark. Spores 

 typical, 16/x X 4:.5/x. 



11. Arthonia varia. Thallus rudimentary, light- 

 gray. Apothecia distinct, linear, not branching. 

 Spores typical, 15/x X 3/x. 



6. Mycoporum. 



This is a small group whose position is rather un- 

 certain. It is evidently closely related to the Graphid- 

 acecB. 



The thallus is rudimentary and begins its develop- 

 ment below the surface of the substratum. It, how- 

 ever, soon breaks through, forming a deficient crus- 

 tose thallus. The algae are perhaps Protococcus, 

 though they also have a resemblance to Pleurococus. 



The apothecia are irregular in outline but never 

 distinctly linear. Disk and hypothecium are black. 

 The spores are large, eight in number, multilocular, 

 colorless to brownish, and constricted at the middle. 



The few representatives occurring in the United 

 States seem to be southern in their range, occurring 

 upon trees. 



1. Mycoporum pycnocarpum. Thallus deficient, 

 evenly spreading, grayish. Apothecia small, scat- 

 tered, irregular in outline, scarcely raised above the 

 thallus and substratum. Spores large, multilocular, 



