PLACODIUM | PHYSIACEX 215 
21. Pl. chalybeum Naeg. ex Hepp Flecht. Eur. n. 204 
(1853).—Thallus thickish, spreading, or tending towards a 
definite outline, closely adnate, deeply cracked-areolate, whitish- 
or greyish-lead coloured, the outer areolations sometimes crenulate, 
generally limited by a black hypothallus (K + pale-violet). 
Apothecia small or moderate in size, immersed or adnate, plane, 
the disc black, dull-brown when moist, naked (or pruinose ?), the 
thalline margin, when visible, entire, whitish (K + slightly pale- 
violet in section); paraphyses clavate, branched and septate 
upwards, brown at the tips; spores ellipsoid, 11-15 yp long, 
6-8 p thick, polarilocular.—Mudd Man. p. 134; Cromb. Lich. 
Brit. p. 46; Leight. Lich. Fl. p. 179; ed. 3, p. 165. Parmelia 
chalybea Fr. Lich. Eur. p. 125 (1831). Lecanora chalybewea 
Scher. Enum. p. 60 (1850); Cromb. in Grevillea xviii. p. 46 
(1889) & Monogr. i. p. 390. 
Easicc. Cromb. n. 59; Johns. n. 314. 
Easily recognized by the colour and by the regular deep areolation 
of the limited thallus. There is only a very faint violet reaction in 
the apothecium with potash, but spores and paraphyses are charac- 
teristic of Placodiwi. 
Hab. On calcareous rocks in maritime and hilly regions.—Distr. 
Rare in S.W. and N. England, N. Wales‘and the Grampians, Scot- 
land.—B. M. Babbicombe, Devon; Llanymynech Hill, Shropshire ; 
Great Orme’s Head, Carnarvonshire; Penhill, Yorkshire; Burnhope, 
Weardale, Durham; Whitbarrow, Westmoreland ; Craig Tulloch, 
Blair Athole, Perthshire. 
22. Pl. variable Nyl. Lich.-Scand. p. 138 (1861).—Thallus 
thinnish, determinate, limited by a black hypothallus, cracked- 
areolate, dark- or brownish-grey (K + pale-violet). Apothecia 
somewhat prominent, rather small, plane or convex, the disc 
brown or blackish, generally densely bluish-grey pruinose, the 
thalline margin prominent, entire, whitish; paraphyses sub- 
clavate, septate upwards ; spores ellipsoid, 13-16 p long, 7-10 p 
thick (epithecium K + pale-violet).—Cromb. in Journ. “Bot. viii. 
p- 97 (1870); Leight. Lich. Fl. p. 179; ed. 3, p. 165. Lichen 
variabilis Pers, in Ust. Ann. Bot. vii. P. 26 (1794). Lecanora 
variabilis Ach, Lich. Univ. p. 369 (1810); Cromb. Monogr. i. 
p. 391. 
Closely allied to the preceding, of which it might be only a 
variety. It differs in the darker ealour of the thallus, “the superficial 
apothecia and the pruinose disc. 
Hab. On calcareous rocks in hilly districts.x—Distr. Rather rare 
in W. and Central England and in W. Ireland.—B. M. Bathampton 
Downs, Somerset ; Ablington and Grove Lane, Cirencester, Gloucester- 
shire; Buckingham; Ampthill, Bedfordshire; Llanymynech Hill 
Shropshire ; Cunning Dale, Buxton, Derbyshire. 
Var. ecrustaceum Nyl. tom. cit. p. 139.—Thallus immersed in 
the rock, scarcely visible. Apothecia small, subinnate, the 
