Rev. W. A. Leighton on neiv British Arthonise. 331 



round, very variable in size, either single, or several arising as 

 elevated rounded spots on different portions of the sui'face of 

 the hymeniuni oi Lee. (/laucoma, ultimately becoming confluent, 

 and entirely covering it, thus rendering it abortive, and giving 

 it the general appearance of a black disk with a white irregular 

 wavy thalloid margin. Disk roughish, somewhat flattened or 

 more or less convex, without any margin, of an opake brownish- 

 black. A vertical section shows the parasite occupying the 

 upper portion of the hymenium, obliterating all traces of the 

 paraphyses and asci of L. glaucoma, and leaving its pale yellow 

 hypothecium alone free. Hymenium of a pale brown colour, 

 with numerous obovate or pyriform asci imbedded in a compact 

 mass without any appearance of paraphyses. Iodine turns the 

 Arthonia of a deeper brown, but the hypothecium of L. glau- 

 coma of a blue colour. Sporidia in asci, eight, oblong, normally 

 with three septa, frequently with two only, and sometimes with 

 only one ; the cells either empty or filled with minute rounded 

 granules, colourless or pale yellow. 



Our specimens were identified by Dr. Nylander*. 



Plate XI. tig. 1. Thallus of L. glaucoma with the Arthonia on the apo- 

 thecia : nat. size. Fig. 2. The same, magnified. Fig. 3. Vertical 

 section of apothecium of L. ylaucoma, showing Arthonia glauco- 

 maria parasitic in the upper portion of hymenium. Fig. 4. Ascus 

 and sporidia of A. (jlaucomaria, magnified. Fig. 5. Sporidia, more 

 highly magnified. 



2. Arthonia vinosa, Leight. Thallus thin, membranous, 

 smooth, pale brown, subdeterminate ; ardellse sessile, irregularly 

 roundish ; disk deep vinous red, convex, dull ; sporidia in asci, 

 eight, large, obovate, uniseptate. 



Arthonia vinosa, Leight. Lich. Brit. Exsic. 224 ! (1856). 



On oaks : Newton Wood ! Stagdale ! and Oggeray Gill! Cleve- 

 land, Yorkshire, Mr. W. Mudd. Nessclifl"e Hill, Shropshire ! 



Thallus forming irregular patches of greater or less extent, 

 .ind of various form, of a cheerful pale brownish hue varying in 

 intensity, on the bark of oaks. Ardelloi minute, variable in size, 

 roundish, oblong and irregular in form, single or confluent, 

 more or less raised or convex, especially on older barks, whilst 

 on younger barks they are scarcely raised and almost flat. On 



* Dr. Nylander in his Syn. Arthoniarum quoted above, says of his 

 A. parasemoides, wliich he states to occur on the apothecia of Lecidea para- 

 sema, Ach., and also on Lecanora glaucoma, Ach., " ex Anglia candem 

 misit rev. Leighton." I know not to what plant he refers. lie charac- 

 terizes A. parasemoides thus: "Thallus nullus, apothecia parasitica hyme- 

 nicola atra convexiuscula, intiis albida vcl nigricantia ; spora; 6-8"* ovoideae 

 1 -3-septat8e, gelatina hym. iodo sordide rubescens." 



