74 LICHENES. 



in form, nearly plane, not bordered, within somewhat gelati- 

 nous, covered by a dark membrane. 



19. Opegrapha. Thallus crustaceous, membranaceous or 

 leprous, uniform. Apothecia oblongo-elongated, immersed or 

 sessile, covered by a dark membrane, the disk narrow, with a 

 proper border. 



* * * Apothecia discoid, round, sessile, or at length emerging. 

 f Thallus (in a moist state) gelatinous. 



20. Collema. Thallus of the same nature throughout, when 

 moist gelatinous, when dry hard and cartilaginous, sometimes 

 foliaceous. Apothecia orbiculate, sessile, (rarely on podetia), 

 bordered, formed entirely of the thallus. 



f f Thallus crustaceous. 



21. Variolaria. Thallus crustaceous, or cartilagineo-mem- 

 branaceous, uniform. Apothecia verruciform, formed of the 

 thallus, bearing a powdery or flocculent substance which covers 

 the disk. 



22. Lecidea. Thallus crustaceous, uniform or scaly. Jlpo- 

 thecia orbiculate, sessile, the dish coloured, the border of the 

 same colour as the disk. 



23. Urceolaria. Thallus crustaceous, uniform. Apothecia 

 orbiculate, immersed in the thallus, the disk concave, the border 

 formed of the crust. 



24. Lecanora. Thallus crustaceous, uniform, or lobed and 

 scaly at the margin. Apothecia orbiculate, sessile, their margins 

 formed of the thallus, tumid, elevated. 



fff Thallus foliaceous, or membranaceous. 



25. Parmelia. Thallus foliaceous or membranaceous, stel- 

 lato-lobate or laciniated. Apothecia orbiculate, exteriorly be- 

 neath, as well as their margins, formed of the thallus, the disk 

 concave coloured. 



26. Sticta. Thallus foliaceous, or coriaceo-cartilaginous, 

 hirsute beneath, and there furnished with hollow or bare spots, 

 (cyphellce). Apothecia orbiculate, sessile, exteriorly beneath, as 

 well as their margins, formed of the thallus, the disk concave, 

 coloured. 



27. Solorina. Thallus foliaceous, coriaeeous, lobed, free, 

 beneath having fibrous veins. Apothecia subrotund, sessile, not 

 bordered. 



28. Peltidea. Thallus foliaceous, coriaceo-membranaceous, 

 lobed, having woollv veins beneath. Apothecia borne on pro- 



