Syncesia.] LICHENES. 103 



On the bark of trees, common ; also on siliceous rocks. The charac- 

 ters given of T. melaleucum, Turn, and Borr. seem to apply to states 

 of this species, which varies in the colour of the thallus, in its tenuity, 

 in the degree of inflection of the thallodal margin of the warts, in the 

 elevation of the warts, as well as in the lighter or deeper colour of the 

 disk. In the rock variety, the y. scutelliforme of Ach. the thallus is 

 often much dispersed into white, tartareous, lobed, and crenate scales ; 

 these, as well as the exterior shell of the apothecium, are cancellated 

 and rough with minute points and depressions ; the nucleus is whitish, 

 semitransparent, and gelatinous when wet, having erect bundles of 

 filiform cells, whose summits, protruding above the disk, constitute the 

 pruinose appearance; among these cells may be seen most minute 

 dark points. In all states of this species occasionally two and even 

 three nuclei may be seen within the same wart. 



2. T. exanthematicum, ACH. Thallus subtartareous, very 

 thin, continuous, grey; warts of the apothecia half immersed, 

 hemispherical, with a radiated orifice ; the disk concave, flesh- 

 coloured. Ach. L. Un. p. 313. Eng. Bot. t. 1184. 



On limestone, near Belfast, Mr. Templeton ; common in the 

 South. The surface of the thallus often has a sanded appearance. 



3. T. Hutchinsice, BORR. " Thallus very white, warts of the 

 apothecia crowded, obsolete, of irregular figure, at length ex- 

 panding with a broken, flocculose, inflexed orifice ; the nucleus 

 forming a dark, grey, pruinose, concave disk, with a white, 

 lacerated margin." Borr, in Eng. Bot. Supp. t. 2652. 



On moss, near Bantry, Miss Hutchins. The disk is greenish-grey, 

 covered with white pruina, concave ; the nucleus, nearly colourless, 

 pellucid, gelatinous, deep, and round beneath, is contained in cortical 

 matter, indurated into a membrane, rising above the surface of the disk 

 and forming the characteristic mark of the genus. The structure of 

 the apothecia of Thelotrema lepadinum is very different. 



* * Apothecia) (lirellce,) sublinear. 

 17. SYNCESIA. 



Thallus crustaceous. Apothecia oblongo-elongate, stellate- 

 radiate, aggregated and immersed in scattered thallodal ver- 

 rucce. Perithecium none. Lamina proligera pellucid, sup- 

 ported on opaque vertical layers. 



However averse to offering a new genus among the lichens, I found 

 it impossible to arrange the present under any described. It ap- 

 proaches Arthonia in character but not in habit. It bears to Arthonia 

 the relation of Porina to Verrucaria, but is still more distinct by the 

 presence of opaque immersed stipites to the apothecia : these plates 

 appear to have a fibrous structure in a vertical direction : they remind 

 one of the blackish brown matter on which the lamina proligera of 

 certain Lecanorce and Lecidece rest. 



1. S.albida. 



On dry shaded rocks between Dunkerron and Killarney, County of 

 Kerry. Thallus from five to eight inches in diameter, tartareous, thin, 



