LECIDEA. 



235 



interior is divided into labyrinthine cavities. The sterigmata 

 are very slender ; the spermatia of great tenuity, and straight. 



Genus II. LECIDEA, Ach. 



Gen. Char. Thallus effigurate or uniform. Apothecia gene- 

 rally black, flattish, marginate, thalamium frequently becoming 

 tumid and covering margin of exciple, which is generally carbo- 

 naceous and very black. Tissue on which thalamium rests com- 

 monly also carbonaceous, sometimes differently coloured. (Name 

 from Ackos, a dish, and ctSos, like, in allusion to the form of the 

 apothecia.) 



A large and important genus, including most of the 

 small crustaceous Lichens of our rocks and walls, — those 

 species which are generally the initial agents in the disin- 

 tegration of our mountains and in the formation of vege- 

 table soil. Many species appear destitute of a thallus, the 

 dissociated elements of which however may be found sunk 

 in, or incorporated with, the surface of the rock or tree on 

 which they grow ; some sink their apothecia deeply in the 

 hardest rock."* 



* For minute anatomy of species of Lecidea, vide Dr. Schuchardt, in 

 'Botanische Zeitung/ March 2, 1855. 



