H5 



The genera representing this family are southern in their distribu- 

 tion, though some species are very common throughout the territory, 

 as for example Grafhis scrij>ta. They generally occur upon the 

 smooth bark of trees. Some of the southern species reach a high 

 development in the thickness of the thallus, though the structure re- 

 mains quite simple. 



Key to the Genera. 

 Spores 2-8-celled, or simple. 



Spores 2-celled, colorless. i. Hazslinskya. 



Spores 4— 6-celled, acicular, colorless. 2. Opegrapha. 



Spores S-celled, large, oblong, colorless. 3. Gr aphis. 



Spores simple, colorless. 4. Xylographa. 



Spores 4-celled, not acicular. 5. Arthonia. 

 Spores multilocular. 



Spores constricted in the middle. 6. Mycoporum . 



Spores not constricted, colorless. 7. Arthothelium . 



1. Hazslinszkya Kbr. Parerga Lich. 257. 1865. 



This is another doubtful and lowly organized genus of lichens 

 represented by only a few species which have been found in Europe 

 as well as the United States ; the American forms or form have been 

 included under Opegrapha as O. demissa. 



The thallus as well as the apothecia begin their development be- 

 low the surface of the substratum ; after a time the thallus forms a 

 thin whitish film over the substratum ; it never forms more than a 

 mere network of hyphae in which clusters of algae are suspended 

 ( Cystococcus humicola and perhaps Pleurococcus vulgaris) . There 

 is no differentiation into layers ; the rhizoidal hyphae extend into the 

 substratum to a considerable depth. 



The apothecia soon break through the thin layer of the superim- 

 posed substratum and appear as minute black dots ; upon examina- 

 tion with a lens they appear more or less orbicular or somewhat elon- 

 gated with irregular outline ; the disk is flattened. The epithecium 

 and upper ends of the simple more or less granular paraphyses are 

 dark in color. The hypothecium (perithecium) consists of a close 

 network of more or less brownish hyphae. 



The spores are colorless, of medium size and distinctly two- 

 celled, one cell being larger than the other^ constricted at the sep- 

 tum ; the spore-wall and septa are thin. 



As far as known the species occur upon trees in the north tem- 

 perate zone. 



