J. A. MARTINDALE : NOTES ON BRITISH LICHENS. 297 



the publication of the third edition of the Lichen Flora of Leighton. 

 The case is somewhat different if we consider the nine or ten 

 members of the group which, though occurring on the Continent, 

 have not yet been discovered within the limits of the British Isles. 

 Of these latter the majority are new species, though all but two had 

 been named before the appearance of Leighton's latest edition. 



The eight British species, and the dates of their first recognition, are 



1753. Parmelia olivacea (Linn., Species Plantarum). 



1803. Parmelia prolixa (Ach., Methodus). 



1 8 10. Parmelia exasperata (Ach., Lich. Universalis). 



1 8 10. Parmelia sorediata (Ach., Lich. Universalis). 



1829. Parmelia Delisei (Dub, Bot. Gall.). 



1830. Parmelia fuliginosa (Fr., in Dub. Bot. Gall.). 

 1873. Parmelia subaurifera (Nyl, in Flora). 



1875. Parmelia isidiotyla (Nyl., in Flora). 

 Now, since 1830, by which year six of these plants had been 

 described, there have been published in England, Hooker's ' English 

 Flora' (1833), Mackay's 'Flora Hibernica' (1836), Mudd's Manual 

 (185 1), and Crombie's 'Lichenes Britannici' (1870). Yet in Hooker's 

 and Mackay's Floras only one plant is described styled ^ olivacea as 

 if it was a homogeneous species, one and indivisible — not the slightest 

 hint being given that it was made up of a number of very different 

 forms. And it is to be observed that this apparent homogeneity of 

 the species is not to be accounted for by the overwhelming prepon- 

 derance of one form and the extreme rarity of the others, so that all or 

 nearly all specimens collected belonged to that one form. Even as 

 early as the time of Dillenius, four of the forms had been gathered, 

 and were delineated in the ' Historia Muscorum ' (1741), nay, even 

 divided into two species, the first consisting of three varieties. The 

 plants drawn on Plate 24, f. 77, according to Mr. Crombie, who 

 has critically examined the Dillenian Herbarium, are P. olivacea^ 

 P. fuliginosa and P. subaurifera^ while fig. 78 is i^. exasperata. 



In Mudd's Manual there was still only one species recognised, 

 but to it were assigned two varieties — aqjiiloides ( — Delisei) and 

 furfuracea ( = fuligi?iosa). In Crombie's ' Lich. Britannici,' prolixa 

 and exasperata are recorded, in addition to olivacea and fuliginosa^ 

 but Delisei is omitted, probably being included in prolixa. When we 

 come to Leighton's Flora, we find all the species except sorediata^ 

 subaurifera, and isidiotyla. In this work the five forms recognised 

 are grouped in three species, exasperata and prolixa being regarded 

 as varieties of olivacea. It is probable that subaurifera lies hid 

 under fuliginosa and its variety, and very likely British specimens of 

 sorediata and isidiotyla had not been seen by the author. 



Oct. 1887. 



