rhizocjarponJ lecideace^ 195 



scattered irregularly over the thai] us, rarely in indistinct lines, 

 sometimes innate and circumscissed as in the species. — Lecidea 

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

 cxcentrica Nyl. Lich. Scand. p. 234 ; Crouib. 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 DlpIotoiuDia 

 calcareum). 



Hah. On calcareous rocks. — Distr. Somewhat rare throughout 

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

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

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

 Morrone, Braemar, Aberdeenshire. 



10. Rh. confervoides DC. 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. — Mh. petrseuni 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) (exci. 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 vernicu- 

 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 Be Candolle, 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 in their reaction to 

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

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

 of Rli. confervoides in the British Museum give no rea,ction with 

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

 to represent various states of the thallus : in f. albicans {Eh, pctra'um 

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

 crowded, almost concealing the hypothallus ; in f. ciwrcnni (Flot. l. c. ), 

 often found on stones and flints, the fimbriate hypothallus spreads 



O 2 



