LKCAXOKA.] LECANO-LECIDEEI. 359 



1 1. L. murorum Ach. Lich. Univ. (1810) p. 443 ; Nyl. Flora, 

 1883, p. 106. Thallus orbicular, closely adnate, usually whitish- 

 suffused, subrimoso-areolate in the centre, plicato-radiose at the 

 circumference, vitelline-yellow or citrine; radii somewhat turgid, 

 crenate and often also inciso-plicate at the apices (K + purplish). 

 Apothecia moderate, plane or convex, tawny-yellow, orange- 

 coloured or concolorous with the thallus (K -|- purplish) ; the 

 thalline margin entire, paler or concolorous ; spores 0,009-15 mm. 

 long, 0,004-7 mm. thick. Cromb. Grevillea, xviii. p. 44 ; Hook. 

 Fl. Scot. ii. p. 50 pro parte; Tayl. in Mack. Fl. Hib. ii. p. 140 

 pro parte. Pliicodium murorum Leight. Lich. Fl. p. 175 pro parte, 

 ed. 3, p. 161 pro parte ; Cromb. Lich. Brit. p. 45 pro parte ; Mudd, 

 Man. p. 132 pro parte ; Gray, Nat. Arr. i. p. 447 pro parte. Squa- 

 maria murorum Sin. Eng. Fl. v. p. 194 pro parte. Lichen murorum 

 Hoffm. Enum. (1784) p. 63 ; Eng. But. t. 2157 (lower fig.). Lichen. 

 Jtauescens Huds. Fl. Augl. p. 445 pro parte. 



A species until recently little understood and very imperfectly limited, 

 so that the trivial name of murorum, as applied to it by British and other 

 authors, is, to a great extent, a nomen vagum. It appears under two con- 

 ditions of growth a larger, with the thallus more developed and extended 

 (var. (3 nvijor Wahl. Fl. Lapp. p. 416) ; and a smaller, with the thallus 

 rosulate and stunted (var. pulrinata Mass. Symm. Lich. p. 13). Both 

 states are usually well fertile, the apothecia being numerous and often 

 crowded. The spermogones have the spermatia oblongo-bacilliform, 

 0,030-35 mm. long, 0,007-9 mm. thick. 



Hab. On calcareous rocks and mortar of walls in maritime and lowland 

 districts. Distr. No doubt general and common, though seen only from 

 a few localities in Great Britain. B. M. : Glynde, Sussex ; Anstey's Cove, 

 Torquay, S. Devon ; St. Austell, Cornwall ; near Cirencester, Glouce^ter- 

 shire ; Great Or me's Head, Carnarvonshire; Teesdale, Durham : Wark- 

 worth Castle, Northumberland. Morningside, near Edinburgh; Appin, 

 Argyleshire ; near Aberdeen. 



Var. /3. corticicola Nyl. Bull. Soc. Bot. t. xiii. (1866) p. 366. 

 Thallus smaller, more contracted and less developed, vitelline-yellow 

 or greyish-green. Apothecia numerous, congested ; spores (often 

 subsimple) 0,011-15 mm. long, 0,005-7 mm. thick. Cromb. 

 Grevillea, xviii. p. .Brit. Exs. : Larb. Lich. Hb. n. 52. 



From the structure of the spores probably referable rather to the next 

 subspecies, a.? suggested by Dr. Arnold (Flora, 1875, p. 153), though al>o 

 approaching subsp. L. tegularis in external aspect. The plant, as described 

 by Nylander, differs from the British specimens in the thallus being 

 greyish-green, when the reaction with K is less distinct. 



Hub. On the trunk of an elm and on old timber in lowland districts. 

 Distr. Apparently very rare in S. and E. England. B. M. : Windsor 

 Great Park, Berkshire ; Great \Villbraham, Cambridgeshire. 



Subsp. 1. L. decipiens Xyl. Flora, 1869, p. 81 (nota), 1883, 

 p. 106. Thallus moderate, crowdedly verrucose in the centre, the 

 vcrrucac often efflorescent with concolorous sorcdia, peripheral radii 



