Placodium.} L1CHENES. li)7 



On flat calcareous stones, Suffolk, Cambridge and Westmoreland. 

 On encrinal limestone rocks, near the new bridge below Barnard-Castle, 

 Durham, Mr, Winch. Scotland. 



19. S. saxicolu, {radiated wall Sqtmmaria\ tliallus orbicular 

 finely lobed somewhat imbricated pale sulphureous-green, the 

 lobes cut crenate zigzag and entangled, apothecia central crowd- 

 ed flatfish tawny-brown with a pale uneven border — Lecanora 

 mxicola, Ac//. Syn, p. 180. — Lichen saxic, Ach. Prodr. — E. Bot. 

 1. 1695. — L. muralis, Dicks. — Psora muralis, Hojfm. 



On rocks, brick-walls and loose flinty stones, in exposed situations. 



20. S. ehcina, (orbicular olive Squamaria); thallus orbicular 

 imbricated depressed stellated membranous dark greenisb-olive 

 smoothish and of* the same colour beneath its segments close- 

 pressed pinnatifid linear obtuse, apothecia central brownish- 

 black with an elevated border Parmelia ehcina, Wahl. — 



Ach. Syn. p. 200. — Lecanora ehcina. Ach. Licit. Univ. — Lichen 

 ekeinus, Wahl. Lapp. p. 425. t. 28. / 3. E. Dot. t. 2158. 



Not rare, on the bark of Elms and Fruit-trees, sometimes on flint 

 nulls, Sussex. Mr. Borrcr. On walls and trees, about Norwich, Sir J. 

 E, Smith. 



17. Placoditm, Fee, (part of Placodium, De Cand.). Pla- 

 codium. 



Thallus defined, orbicular and stellated, the scales adherent, 

 indistinct, pulverulent, foliaeeou* in the circumference. Apo- 

 thecia (patellulai) usually in the centre of the thallus. bordered, 

 the border of the same colour as the disk. — Named from tt'/.u^ 

 tt/.u'/.g;, a crust or leaf. — The species of this genua <1<> hoi rank 

 well with Psora, whose thallus is formed of distinct or very 

 slightly combined scales or tubercles, nor yet with Lecidea, whose 

 crust i^ ^till more different. They have indeed the fructifica- 

 tion of Let Hdea with the thallus of Squamaria, or in 1 species, 

 i P. <l,, faleum) almost that of Parmelia. 



J. P.canescens, DeCand. (grey 'J'n< Placodium); thallos ad- 

 oate orbicular often confluent plaited and lobed at the margin 

 with powdery spots of a glaucous- white in the centre, apothecia 

 central depressed black with a narrow border. — Lecidea cants* 

 cens, Ach. Syn. />. 54. — Lichen eaneseens, Dicks, Cr. Fate. 1. 

 /;. Hi. /. 2./. 5. Dill. Mux. t. 18./ 17. A. 



()n trees in England, more rarely <>n rock-. <>u walla and rooft, and 

 rarely producing apothecia, 



2, P. plumbeum, (lead-colowred spongy Placodium)} thallos 

 orbicular livid lead-colour broadly Lobed ami notched and some- 

 what imbricated at tin- margin thick often covered in the 

 centre with grey granulations, clothed beneath with bluiah- 

 blaek ipongy fibres, apothecia central small flat rust-coloured 

 with a \, t \ obscure border. Parmelia phtmbea, Ach. Syn. 

 />■ 2 'hi plumbeus, Light/. Scot. /-. I - 



/ />'"/. (. 85 ■ > "/< w, /,v / ■ 



