pnrsciA.] pnYsciEi. 315 



15. P. melops Duf. (sub Pnrmelia) e.v Xyl. Flora, 1S74, p. 10.— 

 Thallus orbicular, stellari-appressed, mulfifido-laciniatc, more or less 



caesio-greyish ; laciniae narrow, contiguous, convex (K^yellow, 



CaCl~). Apothecia small, plane, the thalline margin entire or at 



length slightly crenulatc ; spores as in tlie preceding species. — 

 Cromb, Journ. Bot. 1885, p. 1JJ5. 



Closely allied to P. aipolia, from wliich it differs chiefly in the darker 

 caesious thallus. Our single British specimen is sterile, with the thallus 

 not well developed. According' to Nyhiiider /. c. it is a widely distributed 

 saxicolous plant iu the mouutainous regions of Europe. 



Hab. On a calcareous wall among dead mosses in a maritime moun- 

 tainous district. — Dt'sfr. Seen only in the S.W. Highlands of Scotland ; 

 no doubt to be detected elsewhere. — B. M. : Appiu, Argyleshire. 



K). P. tribacia Xyl. Flora, 187-1, p. 48. — Thallus orbicular or 

 subeffuse, moderate, shortly laciniate, glaucous-white or white, 

 sprinkled with small, subglobose, concolorous soredia, usually slightly 

 subfarinaceo-suffused : beneath whitish, with a few concolorous 

 fibriUose rhizinaj ; laciniae crowded, imbricate, digitato-crenate at 



the apices (K_-^ **^^, CaCl~). Apothecia moderate, scattered, 



blackish, the thalline margin subentire or suberenulate ; spores 

 oblong, 0015-20 mm. long, 0,008-11 mm. thick. — Cromb. Grevillea, 

 XV. p. 78. — Borrcra co-sia /3. trihacea Aludd, Man. p. 107. Sqna- 

 maria tribacia Sm. Eng. Fl. v. p. 194 pro parte. Psoroma trihaciiim 

 Gray, Nat. Arr. i. p. 445. Lecanora tribacia Ach. Lich. Univ. 

 (1810) p. 415. 



A plant little understood by authors, allied to P. stcNaris, with which 

 it agrees in the reactions. It differs, however, in the thallus being 

 generally covered with a thin farina, in the presence of soredia, and in 

 the more crowded laciuiiie being digitately crenate at the apices. In the 

 soredia it approaches P. c<esia, but differs in all other essential characters. 

 The apothecia are not present in the British specimens (cfr. Ach. /. c). 



Hah. On fruit-trees of orchards in maritime districts. —Distr. Confined 

 to a few localities in S. England and the Channel Islands. — B. M. : St. 

 Martin's, Island of Jersey. Lymington, Hants ; near I'enzance, Cornwall. 



17. P. tribacoides Xyl. Flora, 1874, p. 307. — Thallus orbicular, 

 small, shortly laciniate, -whitish, sprinkled with small, subglobose, 

 white soredia, sparingly subfarinaceo-suffused ; beneath whitish, 

 nearly naked ; laciniae narrow, crowdedly imbricate, digitato-crenate 



at the apices (K^ycUow, CaCl~). Apothecia not seen rightly 



developed. — Cromb. Grevillea, iii. p. 22 ; Leiarht. Lich. FI. ed. 3, 

 p. 140. 



Subsiuiilar to the preceding species, from which, besides other charac- 

 ters, it at once differs in the reaction of the medulla with K. In the 

 specimen gathered there are only two young apothecia. 



