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b. Placodium. Hill. Thallus ad ambitum slellato- 

 radiatus, centro rimoso-areolatus, 



c. Rinodina. Ach. Thallus uniformis. 



13. Urceolaria. Ach. Apothecium scutellare, sessile, 

 superficiare; thalamium constanter denudatum, margina- 

 tum, concavum vel planum, ab excipuli limbo subdiscre- 

 tum, atrum vel rufescens. 



14. Dirina. Fr. Apothecium scutellare, sessile, super- 

 ficiare; thalamium strato thallodeo primum velatum, dein 

 denudatum, planum, atrum. 



Ordo 3. Patelliferi. 

 A. Patella orbiculata; discus &quabüis. 



15. Gyalecta. Ach. Apothecium patellare, urceola- 

 tum, immarginalum. Thallus crustaceus, uniformis. 



16. Lecidea. Ach. Apothecium patellare, planum, 

 marginatum, margo a thalamio sensim intumescente saepe 

 obvallatus. Thallus crustaceus. 



a. P s o r a. Hall. Thallus squamulosus, squamulis ssepe 

 in crustam vajie plicatam confertis. 



b. Rhizocarpon. Ram. Thallus : subiculum atrum, 

 tenuissime fibrillosum, areolis coloratis distinetum; areo- 

 lis interdum in crustam rimoso-areolatam, nigro-limitatam 

 confertis. 



c. Catillaria. Ach. Thallus uniformis, 'Simplex. 



R. Patella elongata, disco rimali vel varie plicato dehiscens. 



17. Opegrapha. Humb. Apothecium patellare, pri- 

 mum orbiculatum, dein ovatum vel lineare; disco ab in- 

 flexis excipuli marginibus rimali. Thallus crustaceus. — 

 Obs. Thalamia ssepc excipulo orbata, hinc immarginata, 

 difformia et radiato-stellata. (Arthonia Ach.) 



