RHIZOCARPOnJ LEClDBACBffi 195 



scattered irregularly over the thallus, rarely in indistinct lines, 

 sometimes innate and circumscissed as in the species. — Lecidea 

 ■petrsea var. excentrica Ach. Meth. p. 37 (1863) ; subsp. 

 excentrica Nyl. Lich. Scand. p. 234 ; Cromb. Lich. Brit. p. 87. 

 L. concentrica var. excentrica Leight. Lich. Fl. p. 350 (1871). 

 L. excentrica Leight. Lich. Fl. ed. 3, p. 379 (1879). 



Exsicc. Larb. Lich. Hb. n. 75; Mudd n. 194 (as Diplotomma 

 calcareum). 



Hah. On oaloareous rooks. — Distr. Somewhat rare throughout 

 the British Isles. — B. M. Jersey ; Builth, Brecknockshire ; Llany- 

 mynech, Shropshire ; Dolgelly and Oader Idris, Merioneth ; Carlton 

 Bank, Cleveland, Yorkshire ; Aohosragan Hill, Appin, Argyll ; 

 Morrone, Braemar, Aberdeenshire. 



10. Rh. confervoides DO. Fl. Franc, ii. p. 565 (1805) 

 emend. (nonMassal.). — Thallus subdeterminate or effuse, often in 

 small patches, greyish-white or -brown, finely areolate, the 

 areolae contiguous or dispersed, convex or depressed, on a thin 

 black spreading often fimbriate hypothallus. Apothecia numerous, 

 moderate in size, black, innate-sessile, plane, with a thin margin ; 

 hypothecium thick, brownish-black ; paraphyses stoutish, lax, 

 clavate and greenish-brown at the tips ; spores oblong, ovate or 

 ellipsoid, at first colourless, becoming dark-coloured, halonate, 

 irregularly muriform, 0,020-38 mm. long, 0,010-17 mm. thick; 

 hymenial gelatine blue with iodine. — Bli. petrxum Koerb. Syst. 

 Lich. Germ. p. 260 (1855) pro parte (non Massal.) ; Mudd Man. 

 p. 220 (excl. vars.). Lecidea petrsea Tayl. in Mackay Fl. Hib. ii. 

 p. 117 (1836) pro parte ; Flot. ex Nyl. in Act. Soc. Linn. Bord. 

 ser. 3, i. p. 374 (1856) (excl. vars.) ; Cromb. Lich. Brit. p. 86 

 (excl. vars.) ; Leight. Lich. Fl. p. 347 ; ed. 3, p. 375. L. amphibia 

 Fr. Lich. Eur. p. 307 (1831) fide Nyl. Lich. Scand. p. 234 (1861) ; 

 Cromb. in Journ. Bot. viii. p. 98 (1870). 



Exsicc. Leight. n. 159, 189 (in B.M. set as Lecidea verrucu- 

 losa) ; Mudd n. 195 ; Larb. Lich. Hb. n. 234 (as var. cinereum) ; 

 Johns, n. 354. 



Has been frequently confused with Lichen petrceus Wulfen as 

 already noted. A leading character, as described by De Oandolle, is 

 the rhizoid-like hypothallus which, along with the often dispersed, 

 mostly flat thalline areolae, distinguishes it from the allied species. 

 The apothecia are usually marginate and sometimes minutely 

 umbonate. 



Nylander (Flora Ixiv. p. 188 (1881) ) and others distinguish two 

 species, morphologically alike, but differing m their reaction to 

 potash. In one no reaction follows, in the other, Bh. eupetrcxiom 

 A. Zahlbr. a yellow colour results followed by red. The specimens 

 of Bh. confervoides in the British Museum give no reaction with 

 potash. Several forms are recorded by Leighton (Lich. Fl. ed. 3, p. 375) 

 to represent various states of the thallus : in f . albicans {Bh. petrceum 

 f. albicans Flot. ex Koerb. I. c.) the whitish thalline areolae are 

 crowded, almost concealing the hypothallus ; in f. cinereum (Flot. I.e.), 

 often found on stones and flints, the fimbriate hypothallus spreads 



o 2 



