GENEKA AND SPECIES. 125 



The present classification will, however, be retained, 

 although RoceMa will be included under Parmeliacece. 

 The Graphidacece are essentially southern in their 

 range, where they also attain their maximum devel- 

 opment ; particularly is this true of Graphis and 

 Arthonia. The thallus is crustose and quite variable 

 in color and thickness. In a large per cent, of the 

 representatives the thallus is hypophloeodal, that is, it 

 occurs below the surface of the substratum and is 

 therefore invisible to the naked eye. The apothecia 

 are characteristic ; instead of being discoid, as in the 

 majority of lichens, they are linear, stellate or ir- 

 regular in outline. They belong to the fungal type. 



KEY TO THE GENERA. 



Spores two to eight-celled or simple, colorless. 



Two-celled 1. Hazslinskya. 



Four to six-celled, elliptical 2. Onegrapha. 



Eight-celled, large, oblong, curved . . . 3. Graphis. 



Simple 4. Xijlographa. 



Four-celled, one end narrowed .... 5. Arthonia^ 

 Spores multilocular. 



Constricted in the middle 6. Mycoporum. 



Not constricted, colorless 7. Art hothel turn. 



1. Hazslinskya. 



A lowly organized group having only a few repre- 

 sentatives. The thallus, as well as the apothecia, 

 begin their development below the surface of- the sub- 

 stratum. The algae are Chroolepus. The apothecia 

 soon break through and appear as minute black dots ; 

 upon examination with a lens they are seen to be 

 more or less orbicular or somewhat elongated, with 

 1 Some of the southern Arthonias have colored spores. 



