OF ARTS AND SCIENCES. 197 



Synopsis of the Genera. 



Div. I. GYMNOCARPI, Schrader, Fries. 



Apothecia open, disciferous. Thalamium originally disciform, or 

 becoming so, contained in a thalline exciple or a proper exciple ; disk 

 normally persistent, ascigerous ; sometimes originally pulveraceous- 

 coUapsed. 



Tribe I. PARMELIACE^E, Fr. — Apothecia rounded, from con- 

 cave becoming explanate, scutelliform, rarely peltate. Disk 

 somewhat waxy, persistent, contained in a thalline exciple. 



Subtribe 1. Usnee^, Eschw. — Disk open. Thallus subvertical, or 

 pendulous-sarmentose, centripetal, without apparent hypothallus. 



1. UsNEA. Apothecia peltate ; thallus with a solid medullary layer. 



2. EvERNiA. Apothecia scutelliform ; thallus fistulous, or with a 



cottony medullary layer. 



3. Ramalina. Apothecia orbiculate-subpeltate ; disk pale, of nearly 

 the same color with the thallus. 



4. Cetraria. Apothecia scutellate-peltate, oblique. 



Subtribe 2. Parmelie^, Eschw. — Disk at first closed, becoming 

 at length discoid-open. Thallus horizontal, centrifugal, with a 

 hypothallus. 



5. Nephroma. Apothecia reniform, adnate to the under side of the 



lobes. 



6. Peltigera. Apothecia peltajform, adnate to the upper side of 



the elongated lobes. 



7. Solorina. Apothecia maculaeform, adnate to the disk of the 



thallus. 



8. Sticta. Apothecia scutelliform ; thallus with cyphellse, or discol- 



ored spots, on the under side. 



9. Parmelia. Apothecia scutelliform ; thallus without veins or cy- 



phellse beneath. 



10. Thelotrema. Apothecia urceolate-scutelliform, a discrete inte- 



rior exciple veiling a rigescent disk. 



11. Gyalecta. Apothecia urceolate, an elevated and discrete colored 



margin bordering a nigrescent disk. 



Tribe II. LECIDEACEiE, Fr. Apothecia rounded, a persistent 



