The genera representing this family are southern in their distribu- 

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

 as for example Gr aphis script a. 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-S-celled, or simple. 



Spores 2-celled, colorless. i. Hazslinskya. 



Spores 4-6-celled, acicular, colorless. 2. Opegrapka. 



Spores S-celled, large, oblong, colorless. 3. Graphis. 



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- Arthotkelium* 



i. 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 Opegrapka 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 hmnicola and perhaps Plenrococciis 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. 



