Lecidea.] 



LICHENES. 125 



Under the lens the disk is scarcely distinguishable from the lamina 

 proligera, but as a dusky surface ; the latter is a narrow layer, 

 very pale brown, semi-transparent, and striated, resting on a dense 

 layer of black matter. The apothecia sometimes resemble crowded 

 lirelltB. 



36. L. immersa, Ach. Thallus tartareous, thin, continuous, 

 whitish, somewhat determinate ; apothecia black, numerous, 

 evenly scattered, flattish or concave, immersed; the disk sub- 

 pruinose ; the border thick. Ach. L. Un. p. 153. Eng. Bot. 

 t. 193. 



On limestone ; not uncommon. The apothecia are not only im- 

 mersed in the thallus, but, by a singular property of this species, and of 

 Verracuria Schraderi, are placed in cavities of the stone formed by 

 some law of the living force as yet unexplained. 



37. L. rivulosa, Ach. ' Thallus tartareous, determinate, 

 cracked, brownish-grey, at length waved and rough ; the bor- 

 der zonate, of an olive colour ; apothecia numerous, scattered, 

 sessile, black, flat; the disk subpruinose; the border waved, of 

 a pale brown. Ach. Meth. 38, Syn. p. 28. Eng. Bot. t. 1737. 



On siliceous rocks ; very common. A number of individuals, sepa- 

 rated by their dark linear borders, give the appearance of the divisions 

 of a map far more strikingly than in L. geographica. Dissection 

 shows the disk of a blackish-olive, which layer re-enters under the 

 apothecium ; beneath the disk is a pale, striated, semi-transparent 

 lamina proligera, of considerable thickness, resting on some white, 

 apparently cortical matter. Fries, in his Lich. exsicc. number 39, 

 makes Lecidea Lightfootii, Ach. (and, probably, justly) a variety of 

 this. 



38. L. pruinosa, Ach. Thallus tartareous, very thin, at 

 length scattered and disappearing, greyish-white ; apothecia 

 flattish, purplish-black ; the disk pruinose ; the border narrow, 

 waved, and distorted. Ach. Meth. p. 55. Eng. Bot. t. 2244. 

 L. albocccrulescens, /3. pruinosa. Ach. L. Un. p. 189. 



On walls, near Belfast, Mr. Templeton ; on granite, near Dublin, 

 not uncommon. Under the lens the disk cannot be distinguished from 

 the lamina proligera ; this appears of a light reddish-brown, becoming 

 paler where it meets some white cortical matter, on which it rests, and 

 which enters the apothecium at its lowest point ; the lamina is semi- 

 transparent and striated. The apothecia sometimes appear immersed 

 below the level of the surface of the lime that exudes from the mortar 

 of walls. 



39. L. speira, Ach. Thallus tartareous, subdeterminate, very- 

 white, cracked, somewhat granulated, rough, with minute ele- 

 vations ; apothecia slightly immersed, flat, covered with a white 

 pruina, at length convex, very black, with a waved border. 

 Ach. L. Un. p. 184. Eng. Bot. t. 18G4. 



On limestone, at Dunkerron Castle. At Portmarnock, near Dublin, 

 is found apparently the same species, but with scarcely any pruina on 

 the apothecia, which are very convex and rugged : this state, I sup- 



