370 LICHENACEI. [LECANORA. 



Hob. On the trunks of old trees in wooded districts. Distr. Only in 

 S. and W. England ; no doubt to be detected elsewhere. B. M. : Wal- 

 thamstow, Essex ; Glynde, Sussex ; near Bradford, Wiltshire ; Windsor 

 Great Park, Berkshire. 



b. Thecae 8-spored. 



25. L. medians Nyl. Bull. Soc. Bot. Fr. xiii. (1866) p. 367. 

 Thallus orbicular, minutely granulose or leproso-granulose in the 

 centre, plicato-radiose at the circumference, opaque, vitelline-yellow 

 or citrine, greyish- white in the centre (K ). Apothecia moderate, 

 plane, sordid-yellow or yellowish-brown (K ) ; the thalline margin 

 entire or crenulate, citrine ; spores oblongo- ellipsoid, simple, or oc- 

 casionally 1-septate, 0,011-17 mm. long, 0,0045-65 mm. thick. 

 Cromb. Grevillea, xviii. p. 45 ; Leight. Lich. Fl. p. 205, ed. 3, 

 p. 189.Placodium medians Nyl. Bull. Soc. Bot. Fr. ix. (1862) 

 p. 262. Brit. Exs. : Larb. Lich. Hb. n. 59. 



Externally subsimilar to L. murorum, to which at first sight it seems 

 allied, but differs in the absence of any reactions and in the structure of 

 the spores. The thallus is at length somewhat expanded, becoming 

 almost leproso-dissolved in the centre, which is inspersed with citrine 

 granules. It is seldom fertile, though when present the apothecia are 

 numerous. 



Abbey, Cambridgeshire. 



26. L. epixantha Nyl. Act. Soc. Linn. Bord. t. xxv. (1864) p. 8. 

 Thallus effuse, thin, granulose, yellow- vitelline or greenish-grey 

 (K ), often subevanescent. Apothecia small, sessile, plane or 

 slightly convex, yellowish-orange or greenish-yellow (K ); the 

 thalline margin thin, subcrenulate, pale-yellow ; spores 8nse, 

 oblong or ellipsoid, simple, at length polari-locular, 0,012-21 mm. 

 long, 0,005-7 mm. thick. Cromb. Grevillea, xviii. p. 45 ; Leight. 

 Lich. Fl. p. 206, ed. 3, p. 213. Lecanora viteUina vars. epixantha 

 et octospora Nyl., Cromb. Lich. Brit. p. 48; var. epixantha Leight. 

 Lich. Fl. p. 181, ed. 3, p. 167. Lecidea epixantha Ach. Licb. Univ. 

 (1810) p. 208. 



Externally scarcely distinguishable from L. viteUina, but differs defi- 

 nitely in the number of the spores. The thallus is entirely absent when 

 the plant grows, as it often does, mixed up with other lichens. At times 

 the thalline margin of the apothecia is at length excluded. 



Hob. On rocks and walls in maritime and upland situations. Distr. 

 Seen only from a few localities in S. England, Wales, and S. Ireland ; no 

 doubt overlooked elsewhere, especially when athalline. B. M. : Hastings, 

 Sussex; Cheddar, Somersetshire; Llandyssil, Cardiganshire. Giant's 

 Stairs, co. Cork. 



