THE ANNALS 



AND 



MAGAZINE OF NATURAL HISTORY. 



[SECOND SERIES.] 

 No. 74. FEBRUARY 1854. 



VIII. — Monograph of the British Graphideee. 

 By the Rev. W. A. Leighton, B.A., F.B.S.E. 



[With four Plates.] 



Graphide^. 



Apothecium oblong or lu-ellseform. Disk at fii'st connivent or 

 veiled^ oblong, subcanaliculate. In a normal state margined 

 with a proper or thallodal margin, or both. 



This is a very extensive tribe of Lichens, and is well marked, 

 in its typical genera, by the peculiar form of the apothecium, 

 which is elongated into a furrow-like form, simple or branched, 

 sessile or immersed in the thallus, and termed a lirella from its 

 shape. This lirella seems in reality to be the patellula of a Le- 

 cidea whose growth has ceased at two opposite sides or points, and 

 been carried on and developed excessively at two other opposite 

 points at right angles to the former. The carbonaceous exci- 

 pulum is either entire, enclosing the sides and base of the lamina 

 proligera, and surrounding the disk with a proper margin, as in 

 Opegrapha ; or is dimidiate and confined to the sides of the 

 lamina proligera, the base being naked, as in Graphis; or disap- 

 pears altogether in the abnormal genera, as Arthonia, by which 

 it approximates to the genus Xyloma of the Fungi. Fries 

 (L. Reform.) regards the plants as deformations of Parmeliacece 

 and LecidiruB, Parmelia and Biatora " in statu atypico," de- 

 forming their apothecia so as to become like those of Leuco- 

 gramma and Ustalia, and Lecidece compressing and elongating 

 theirs similar to those of Opegrapha. In the tropics also Leuco- 

 gramma reverts to th^ type of Parmelia, just as Opegrapha in 

 temperate regions reverts to Lecidea ; whilst Lecanactis oscillates 



Ann. i$ Mag. N. Hist. Ser.2. Vol. xiii. G 



