260 ADDENDA. 



black or purplish colour. The border is hardly apparent, and quite 

 obliterated by age or the application of moisture. Dissection shows 

 the colour of the apothecia arises from the blackish-brown substratum 

 seen through the pellucid lamina ; this is in a very thin layer, is 

 striated, and surmounted by a glaucous disk. 



Page 137! before Lecanora varia, insert — 

 L. albo-flavida. Thallus tartareous, indeterminate, rugoso- 

 granulate, uneven, cracked ; buds in a coarse greenish-ochrey 

 powder. Apothecia sessile ; the disk concave, at length flat, 

 brown-flesh coloured; the border swollen, smooth, inflexed, gra- 

 nulato-crenate. 



On transition rocks, facing the south, Dunkerron ; not uncommon, 

 the apothecia very rare. The habit is of Endocarpon sulphureum, 

 and so the patches are closely adpressed to the rock, often 12 — 24 

 inches in diameter ; but it is the proper thallus that gives the yellow 

 tinge to the surface of the former, while in our plant the paleochraceous 

 hue is altogether borrowed from the buds : these are constantly present, 

 and by their flat subcircular aggregations resemble a Variolaria. The 

 thallus is sometimes in scattered subglobular white grains, which are 

 waved or sublobate, often appearing carious with pits : again the grains 

 are so approximated that the entire surface appears as a rimose crust 

 of a sordid white. The apothecia are large in proportion to the tbal- 

 lodal grains. By dissection we find beneath a pale subopaque disk, a 

 transparent, colourless, striated lamina of considerable thickness, and 

 under it an opaque layer of a brick-red, which gives to the surface of 

 the apothecia a flesh-coloured appearance. Acquainted with this plant 

 for several years, I have been enabled to determine it only within a few 

 days by the tardy discovery of the apothecia. 



Page 1 40, before Lecanora gelida, insert — 

 L. linearis. Thallus of minute, linear, bright-yellow, scat- 

 tered or substellato-aggregate, soft scales, waved and somewhat 

 thickened at one end, on a very thin, pale-brownish substratum. 



On the faces of crumbling slaty stones in dark recesses, Dunkerron 

 mountain. At first sight this minute species might be supposed a Le- 

 praria ; under the lens it has stronger claims to rank among the acha- 

 rian Placodia, for the apparent golden yellow powder scattered on the 

 surface of the stone is found to be composed of linear elevated scales, 

 often clustered and stellate. The apothecia are unknown. 



