192 LICHENES. [Psora. 



powdery with a very thick rounded entire mealy border. Ach. 

 Syn.p. 170. — Lichen Turneri, E. Bot. t. 857. 



Trunks of old oaks and other trees. — Too near perhaps to L. 

 tartarea. 



31. L. citrina, Ach. (lemon-coloured Wall Lecanora); crust 

 leprous powdery indeterminate bright lemon-coloured, apothe- 

 cia scattered sessile minute orange-coloured with a pale yellow 

 powdery border. Sm. — Ach. Syn. p. 176. — Lichen citriuus, 

 Ach. Prodr.—E. Bot. t. 1793. 



On brick and flint walls in Norfolk. On wood, Yorkshire. 



32. L. vitellina, Ach. (yolk of Egg Lecanora); crust leprous 

 granulated indeterminate bright greenish-yellow, apothecia 

 clustered sessile flat tawny- yellow at length convex and 

 brownish the border elevated crenate. Sm. — Ach. Syn. 

 p. 174. — Lichen vitellines, Ehrh. — E. Bot. t. 1792. 



Common on garden-pales, rails, deal boards, &c. 



II. Thallus subfoliaceous, consisting of scales attached to the sub- 

 stance on which they grow and more or less combined. Apothe- 

 cia always bordered and discoid, sessile (patellula). 



Fam. VIII. Squamarie^e. 

 15. Psora. Hoffm. Psora. 



Thallus defined, thick, formed of distinct, flattish or convex 

 tubercles or scales. Apothecia (patellulce) bordered, plane, at 

 length convex, placed at the sides of the scales, the border of the 

 same colour and substance as the disk Name ; -v^w^, a scurf. 



1. P. c&ruleo-nigricans, (black and blue Psora); thallus of ir- 

 regular imbricated tumid powdery greyish warts or scales, apo- 

 thecia black irregular flattish from the margin of the scales at 

 length hemispherical. — Lichen caruleo-nigricans, Lightf — E. 

 Bot. t. 1139. — Lecidea vesicularis, Ach. Syn. p. 51. — Psora vesi- 

 cularis and paradoxa, Hoffm. 



Upon the ground and among rocks. 



2. P. atro-rufa, (red-brown Psora); thallus subcontinuous 

 lobed, the lobes angular smooth imbricated grey-brown, apo- 

 thecia sessile dark red-brown with a narrow border at length 

 confluent. — Lecidea atro-rufa, Ach. Syn.p. 51. Lichen atro-rufus, 

 Dicks. Cr. Fasc. A. p. 2. t. 12. / 4. E. Bot. t. 1102. 



On sandy ground, among Mosses, chiefly in the north of England. 



3. P. scaldris, (olive and black imbricated Psora); thallus imbri- 

 cated often scattered in kidney-shaped lobes or scales ascending 

 distinct pale-olive powdery at the edge and black, apothecia flat 

 irregular black-bordered. Sm. — Lecidea scalaris, Ach. Syn. 



p. 52. — Lichen scalaris, Ach. Prodr E. Bot. t. 1501. — L. leu- 



cnphmts, Dicks. — Psora ostreata, Hoffm. 



