130 GUIDE TO THE STUDY OF LICHENS. 



Species of Nostoc and Sirosiphon (S. pulvinatus) 

 occur parasitically upon many of the Arthonias. 



3. Arthonia quintaria. Thallus rudimentary, partly 

 hypophloeodal, evenly spreading, light-gray. Apothe- 

 cia small, irregular to somewhat linear, scattered. 

 Spores colorless, four to seven-celled, somewhat curved, 

 narrowed toward one end, 24/u, X 7/x. 



4. Arthonia tcediosa. Thallus rudimentary, partly 

 hypophloeodal, evenly spreading, extending over the 

 apothecia in the form of a thin film, light color to green- 

 ish. Apothecia medium, numerous, irregularly stel- 

 late. Disk dark. No spores came to my notice. The 

 spore-sacs were either entirely empty or contained only 

 immature, gelatinized spores. 



5. Arthonia radiata. Thallus much as in A. quin- 

 taria. Apothecia more numerous, larger, irregularly 

 stellate. Spores colorless, four-celled, 17ft, X 4.0/x. 



6. Arthonia punctiformis. Thallus rudimentary, 

 partly hypophloeodal, evenly spreading, light-gray. 

 Apothecia very small, irregular in form. Disk dark. 

 No mature spores came to my notice. 



7. Arthonia polymorpha, Thallus partly hypoph- 

 loeodal, evenly spreading, pale color. Apothecia of 

 very irregular outline, thinly overspread by the thal- 

 lus. Disk dark-brown. No spores seen. 



8. Arthonia lecidella. Thallus distinct, irregularly 

 areolate, light bluish-green ( Chroolepus and Protococ- 

 cus both present). Apothecia rounded, slightly raised. 

 Disk somewhat convex, dark. Spores as in A. as- 

 troidea. 



9. Arthonia glahrata. Thallus quite distinct, some- 



