PLACODIUM | PHYSIACE® 201 
the crenulate margin of the apothecia. The thailus is corticate on 
both surfaces, and, though closely appressed, is easily detached. 
Hab. On slate roofs and on brick walls in inland districts.— 
Distr. Found only here and there in England, probably overlooked. 
—B. M. Near Groombridge, Sussex; near "Stroud and King’s Stanley, 
Gloucestershire ; Gopsall, Leicestershire ; ; Ayton, Clev eland, York- 
shire; Brigsteer, Westmoreland. 
6. P]. murorum DC. Fl. Fr. ii. p. 378 (1805).—Thallus 
orbicular, stellate-radiate, the laciniz closely adnate, continuous 
from the centre, contiguous and somewhat turgid and crenate at 
the circumference, egg yellow or citrine, usually whitish-suffused 
(K + purplish). ‘Apothecia concolorous, plane, becoming convex, 
the thalline margin entire ; spores apa or ovoid, 9— 15 p long, 
4-7 p thick.—S. F. Gray Nat. Arr. i. p. 447 pro parte ; Mudd 
Man. p. 152 pro parte; Cromb. Lich. Brit. p. 45 pro parte; 
Leight. Lich. Fl. p. 175; ed. 3, p. 160 pro parte. Lichenoides 
erustosum, orbiculis et scutellis flavis Dill. Hist. Musc. p. 136, t. 18, 
fig. 18 c (1741). Lichen flavescens Huds. Fl. Angl. p. 445 (1762) 
pro minore parte. L. murorum Hotfm. Enum. Lich. p. 63 
(1784) ; Engl. Bot. t. 2157 (lower fig.). Lecanora murorum Ach. 
Lich. Univ. p. 433 (1810); Hook. Fl. Scot. il. p. 50 pro parte ; 
Tayl. in aes FI. Hib. ii. p. 140 pro parte ; Cromb. Monogr. i. 
p. 359. 
Exsicc. Johns. nos. 97, 405. 
Distinguished from allied species by the turgid lacinie, by the 
more continuous lobate centre, which is often brown-coloured, and to 
some extent by the white pruina. It has frequently been confused 
by older writers with Pl. callopismum, a species well defined by 
spore characters. Though normally in flat orbicular rosettes 
effigurate at the circumference, it may be considerably broken up 
and occur in stunted crowded lobulate patches (Physcia muwrorwin 
var. pulvinata Massal. Symm. Lich. p. 13 (1855) ). 
Hab. On caleareous rocks and mortar of walls in maritime and 
inland districts.—Distr. Probably general throughout the British 
Isles.—B. M. Anstey’s Cove, Torquay, Devon; Glynde, Sussex; near 
Cirencester, Gloucestershire ; Anglesea; Great Orme’s Head, Carnar- 
vonshire; Teesdale, Durham; Warkworth Castle, Northumberland : 
Morningside near Edinburgh; Appin, Argyll; near Aberdeen; Clare 
Island, Mayo. 
Form corticicolum Oliv. Lich. Eur. p. 90 (1909).—Thallus 
in pulvinate patches, reddish-yellow or greyish-green. Apothecia 
numerous, crowded.—Lecanora murorum var. corticicolum Ny]. in 
Bull. Soc. Bot. Fr. xiii. p. 366 (1866) ; Cromb. in Grevillea xviii. 
p. 44 (1889) & Monogr. i. p. 359. 
Ezsicc. Larb. Lich. Hb. n. 52. 
Hab. On trunks of trees or on old timber in inland districts. 
Distr, Apparently rare in S. and E. England—B. M. Windsor Great 
Park, Berks ; Great Wilbraham, Cambridgeshire. 
