GENERA AND SPECIES. 171 



morphologically resemble similar structures of the pre- 

 ceding genus. Sometimes tlie apothecia occur singly, 

 but they also occur in colonies. The perithecium is 

 black. The spores are usually colored dark, four-celled, 

 otherwise resembling those of Trypethelium. 



The representatives of this genus are mostly south- 

 ern in their range. They occur upon the smoother 

 barks. In many the thallus is very rudimentary, so 

 that the algae (Chroolepus) can only be found after 

 careful search. 



1. Pyrenula aspistea. Bark over thallus brown, 

 smooth. Apothecia small, numerous, black. Spores 

 typical, constricted at transverse septa, 17/u, X 8.5/x. 



2. Pyrenulu nitida. Bark over thallus greenish or 

 yellowish-brown. Apothecia larger, fewer, and more 

 scattered than in P. aspistea, black. Spores typical, 

 not constricted, 14/a X 7.5/x. 



3. Conotrema. 



The thallus is in part epiphloeodal, thin, evenly 

 spreading to indistinctly areolate. The alga? are Pro- 

 tococcus instead of Chroolepus. The apothecia are 

 urn-shaped, less hypophloeodal than in Pyrenula and 

 larger. They break through the superimposed bark 

 and have distinct apical pores from which the spores 

 escape. Disk light color. Spores are long, filament- 

 ous, with numerous transverse septa ; when once seen 

 they will not be mistaken. 



The genus requires further study ; only one species 

 has come to notice ; it occurs upon trees, those of 

 the smoother barks, as Betula and Acer. 



