GENERA AND SPECIES. 119 



2. Psora atro-rufa. Thallus of rather small lobes, 

 margin more or less crenate and lobulate, closely 

 adnate to the substratum, color dark. Apothecia 

 medium, sessile, disk slightly convex, dark. Spores 

 simple, colorless, elliptical, 14/a X 5/x. 



3. Psora rufonigra. Thallus-lobes rather small, 

 somewhat ascending, margin wavy and lobulate, 

 upper surface dark reddish-brown to nearly black. 

 Apothecia medium to large, marginal. Disk convex, 

 black. Spores colorless, simple, elliptical, 12/x X 'V- 



4. Psora decipiens. Thallus-lobes usually ascend- 

 ing, closely crowded, margin more or less crenulate, 

 lobed, turned back and white ; upper surface brown 

 to tawny ; white beneath. Apothecia much as in P. 

 icteria. Spores simple, colorless, elliptical, 14/x X C/x. 



5. Psora RusselUi. Thallus-lobes rather large, 

 entire, quite thick and rigid, margin somewhat cre- 

 nate, white, slightly turned up ; upper surface brown- 

 ish, lower surface light color. Apothecia of medium 

 size, usually marginal. Disk convex, brown. Spores 

 simple, colorless, elliptical, 11/x X 4.5/a. 



15. Gyrophora. 



The representatives of this genus are highly inter- 

 esting, both as to size and form and as to the eco- 

 nomic uses to which they have been put in the past. 



The thallus is typically foliose, and varies in size 

 from medium to very large. The smaller thalli may 

 either be single or form a cluster, more or less imbri- 

 cate. No matter what the size of the thallus may be, 

 it is always entire and held to the substratum by 



