PLACODEI. 335 



Series T. Placodei Xyl. Mem. Soc. Cherb. vii. (1355) p. 175. 



Thallus variously crustaceous, sometimes evanescent, rarely en- 

 tirely wanting ; medullary layer, when present, usually cretaceous. 

 Apothecia lecanorine, lecideine or biatorine, or lirellaeform ; para- 

 pbyses discrete or coherent, rarely not distinct. Spermogones with 

 various sterigmata and spermatia. Placodece Nyl. Mem. Soc. Cherb. 

 ii. (1854) p. 13. 



A very extensive series comprehending by far the largest number of 

 Lichens. It is very variable in the characters of the thallus and fructifi- 

 cation, though the tribes of which it is composed are in both these respects 

 related to each other by connecting links. The less developed thallus, 

 the absence of a distinctly filarnentose medullary layer, and the inferior 

 type of the apothecia distinguish it from the preceding series. The thallus 

 is rarely hypophloeodal, and the apothecia are rarely parasitic. 



Tribe XVIII. LECANO-LECIDEEI Nyl. Flora, 1882, p. 458. 



Thallus crustaceous ; laciniate, squamose, granulose or pulveru- 

 lent, sometimes but little visible, occasionally absent ; internally 

 rarely entirely cellular, containing gonidia, rarely gonimia ; hypo- 

 thallus more or less distinct. Apothecia lecanorine, lecideine or 

 biatorine, occasionally difform. Spermogones with jointed or simple 

 sterigmata. 



This comprises the numerous species of the Lecanorei and Lecidcei, 

 formerly in the Nylanderiau arrangement regarded as distinct tribes. 

 They are now, however, more naturally united into a single tribe from 

 the circumstance that in some instances lecanorine apothecia are not to 

 be distinguished from lecideine ; while in certain cases normally biatorine 

 apothecia occur in species otherwise entirely referable to the Lecanorei. 

 The tribe is primarily divided into six subtribes (one of which, Ifeppiei, 

 does not occur in Great Britain), differing from each other in the fructifi- 

 cation. 



Subtribe I. PANNASIEfSyl. Flora, 1882, p. 458. 



Thallus squamulose or granulose, rarely monophyllous, cellular in 

 texture, containing gouimia, which are usually somewhat inonili- 

 form. Apothecia either lecanorine or biatorine, rarely lecideine ; 

 spores 8nse, colourless, simple or variously septate ; paraphyses 

 discrete, often thickish, generally articulate. Spermogones with 

 jointed sterigmata. 



A subtrihe well characterized by the structure of the thallus. Since it 

 contains gonimia it holds much the same position in this as the Feltiycrci 

 in the preceding series, though the texture is otherwise very different. 



56. PANNARIA Del. in Dub. Bot. Gall. (1830) p. 606 ; Kyi. 

 emend. Flora, 1879, p. 360. Thallus laciniately divided or squa- 

 mulose. Apothecia lecanorine ; spores ellipsoid or oblong, simple ; 

 hymenial gelatine variously tinged with iodine. Spermogones with 

 spermatia somewhat short, cylindrical, slightly thickened and obtuse 

 at either apex. 



