92f Rev. W. A. Leighton on the Btitish Graphidese. 



Thallus thin, crustaceous, of an irregular, scaly or crumbly 

 appearance, dirty white. Lirellce numerous, scattered, for the 

 most part short and obtuse, often nearly round or triquetrous, 

 sessile and somewhat prominent, in variously modified oblong 

 or ovate shapes, straight or slightly curved, either plump and 

 bluntly obtuse at both ends, or widened at one extremity and 

 tapered or narrow at the other, smooth, slightly shining, dark 

 brown. Disk varying in width and form according to the shape 

 of the lirella, either an entire narrow slit or trifid, or furcate at 

 one or both ends, more or less open, especially in old age ; mar- 

 gins tumid, rounded, and incurved in a perfect state ; in old age 

 thinner, sharp- edged, and elevated persistently above the ex- 

 panded depressed or concave disk. 



A specimen from Nent Force, Cumberland ! from Mr. W, 

 Robertson in herb. Borrer, on granite, has the lirellse small, round 

 and tumid, or triquetrous, the disk varying much in shape. This 

 may be the var. /3. aporea, Ach. : the form of the lirella and spo- 

 ridia shows distinctly its connection with O. rupesti'is. I have 

 found precisely similar states on the Great Orme's Head, Caernar- 

 vonshire, and on the Eglwsg rocks near Llangollen. 



The specimen of " Lichen simplex, E. Bot., from Rev. Hugh 

 Davies " in herh. Borrer, was a thin slaty rock, on a small darker 

 part of which were scattered a few fragments or frustules of a 

 whitish, smooth, very thin, slightly cracked thallus, growing on a 

 hypothallus of a dark brown or blackish colour, spreading copiously 

 on all sides in a dendritic manner. Imbedded in the centre of the 

 frustules of the thallus was a single minute shield, or sometimes 

 two or three crowded together, dark brown, with a thick prominent 

 margin surrounding a deep very concave disk of similar colour, 

 which, when wetted, swelled and became convex, or at least level 

 with the surface of the margin. A vertical section (see Plate V. 

 fig. 6 a) exhibited the dark brown excipulum, interrupted however, 

 of a Lecidea supporting a lamina proligera, the asci in which 

 were filled with brown oblong sporidia, uniseptate (fig. 6 b), and 

 were so numerous as to give the section a speckled appearance. 

 On other paler and more shaly portions of the specimens were 

 an abundance of irregularly rounded black bodies of various 

 sizes, some as large as poppy seed, others as small as the shields 

 before spoken of. The smaller of these bodies were somewhat 

 like the plump tumid form of a lirella of an Opegrapha ; the 

 generality of the larger kind presented a prominent wrinkled 

 or broken inflexed border or margin, surrounding either a sunk 

 disk or a sunken ring which encompassed a central portion thick 

 and irregularly raised to a level with the margins ; w^hilst others 

 again were gyrate like the apothecia of an Umbilicaria. All 

 were sessile on the naked rock, without the slightest trace or 

 appearance of any thallus. A vertical section (fig. 6 a, 1) showed 



