Rev. W. A. Leighton on the British Graphidese. 87 



that the study of the thecae (asci) of the Grapkidea has convinced 

 him that many of the genera are empiric, and has proved to him 

 that his genus Tliecaria and Glyphis, Ach., before arranged 

 among the Verrucariea, should be added to the Graphidece. He 

 thinks that the genera Coniangium [Spiloma paradoxum, Ach.) 

 and Coniocarpon {Spiloma, Ach.) are improperly placed among 

 the GraphidetB. 



Fries in ' Summa Veg. Scand.' (1846) includes in Gra- 

 vhidecB — 1. Umbilicaria, Hoffm. 2. Opegrapha (comprehending 

 Graphis, Ach., and Opegrapha, Ach.). 3. Lecanactis, Eschw. 

 4. Arthonia, Duf., "genus dubium." 5. Coniocarpon, DC. He 

 omits in the enumeration of the species included under each 

 genus all mention of Opegrapha elegans, dendntica, Lyellii, and 

 Coniangium vulgare, possibly regarding the first as belonging to 

 a distinct genus, and the three latter as referable to Arthonia, 

 Duf. 



Many of the genera above enumerated refer almost exclusively 

 to tropical plants, and are wholly inapplicable to the structure of 

 our indigenous ones. Moreover, Fries declares it to be in his 

 opinion incorrect to consider the plants of temperate zones as 

 species of tropical genera. Considering however that we act in 

 direct \dolation of nature by comprising, as Fries has done, plants 

 of such markedly different structure all under one genus, Ope- 

 grapha, it seems best to give up ourselves to the guidance of 

 nature and follow the path which she may point out. With this 

 principle in view, I have been under the necessity of creating 

 some few additional genera in this already overloaded tribe, in 

 endeavourmg to arrange our indigenous species under genera 

 founded conjointly on the structure of the perithecium, the 

 nature and general character of the thallus, and the sporidia. 



This essay is founded on the microscopical examination of 

 several thousand specimens in the herbaiia of Wm. Borrer, Esq.," 

 F.L.S.; Rev. T. Salwey; Rev. Andrew Bloxam ; the late W. 

 Thompson, Esq. of Belfast, and others, to all of whom my best 

 thanks are offered for their zeal and liberality in communicating 

 specimens; together with those in my own collection. 



It should be observed that the figures of the sporidia in all 

 the species are drawn to the same scale, and consequently are in 

 relative proportion. 



1 . Opegrapha, Ach. 



Apothecium lirellseform, sessile ; perithecium carbonaceous, 

 entire, or surrounding the sides and base ; disk rimseform or 

 canaliculate, suiTounded with a prominent proper margin. Thal- 

 lus crustaccous or membranaceous. 



Name from oirrj, hollow, and <ypa(f>rj, tvriting. 



