Mr. Turner's Descriptions of Eight New British Lichens. 149 



recentis superne tenerrime viridis, non sine flavedine, siccati ci- 

 nereo-glaucescens, inferno dilute fusco-badius. 



ScutellcE visu perrarae, tballi in centro proveniunt, orbiculares, 

 sessilcs, Viciee saliva seminis magnitudine, disco badio, marginc 

 thallo concolore, semper, vel in junioribus, inrlexo, in vetustis 

 crenulato. 



Substantia membranacea, tenuis. 



This Lichen, which, though sufficiently plentiful in many 

 parts of Britain, does not appear to have been noticed by any 

 author, was first pointed out to me by my friend Mr. Borrer, 

 after whom I have taken the liberty of naming it. I have lately 

 sent it to Dr. Acharius and Dr. Swartz, both of whom acknow- 

 ledge it altogether new to them, and a very distinct species. Its 

 appearance is between that of P. saxatilis and P. tiliacea, but 

 most nearly allied to the former of these plants, from which, 

 especially in a dry state, it sometimes requires careful observa- 

 tion to distinguish them. They generally grow intermixed to- 

 gether, and, when fresh, may be known by their colour, which 

 in P. Borreri inclines to a greenish yellow, whereas saxatilis 

 constantly has a dull leaden hue. The under side of P. Borreri 

 is always much more pale, and but thinly scattered over with those 

 black fibres with which P. saxatilis is constantly villous; its 

 mode of growth is in every stage more regularly orbicular, and 

 more closely pressed to the tree on which it grows ; the lobes 

 are seldom divided above half way to the centre, and are regu- 

 larly dilated with rounded apices, instead of being throughout 

 linear and truncated : but what makes the essential character 

 of discrimination between them is, that the thallus of P. Bor- 

 reri is every where even, and destitute of those elevated veins 

 so remarkable and so constant in P. saxatilis; and that the 

 soredia, which in this species are placed upon these veins, as if 



from 



