126 GUIDE TO THE STUDY OF LICHENS. 



irregular outline. The disk * is flattened and dark in 

 color. The spores are colorless, of medium size, two- 

 celled ; one cell larger, constricted at the septum. 



1. Hazslinskya demissa. Thallus partly below the 

 substratum, rudimentary, light color. Apothecia 

 oval, irregular in outline ; single, not in groups, as in 

 the European form H. gibherulosa^ opening by an 

 oval pore. Disk dark. Spores colorless, two-celled, 

 constricted at the septum, one cell larger, 17/a X 8/x. 



This lichen is usually classified as Opegrapha de- 

 missa. 



2. Opegrapha. 



Thallus rudimentary and mostly hypophloeodal, 

 finally forming a thin film over the substratum. 

 The algae are Chroolepus. The apothecia are usually 

 numerous, small, linear, more or less curved, pro- 

 jecting somewhat above the surface of the substratum. 

 Disk black. The hypothecium is also black. The 

 spores are colorless, elliptical to almost acicular, usu- 

 ally four-celled. They occur upon trees. 



1. Opegrapha varia, Thallus finely pulverulent, 

 light-colored, mostly hypophoeodal. Apothecia ellip- 

 tical, oblong to short-linear. Disk black. Spores 

 are four to six-celled, colorless to pale yellow, 

 23/x X 2.5/x. 



2. Opegrapha vulgata. Thallus rudimentary, whit- 

 ish. Apothecia elliptical to distinctly linear, rather 

 small. Spores acicular, indistinctly four to six- 

 celled, colorless, 24/x X 2.5/x. 



1 The term " disk " is scarcely applicable to the irregular apothecia 

 of this family, but will be retained to avoid the necessity of intro- 

 ducing a new term. 



