Rev. W. A. Leighton on the British Graphidese. 89 



gin or sac of the sporidium itself being visible through its slate- 

 colour. 

 Plate I. fig. 2. a, Vertical section of thallus and lirella ; b, sporidia. 



3. 0. saxatilis, DC. Thallus pulverulent, chalky-white ; lirellse 

 prominent, rigid, straight or stellato-divergent, tapering towards 

 each extremity ; sporidia in asci eight, obtusely or subclavately 

 fusiform, 5-, 6- or 7-septate, the central cell the largest, pale 

 yellow. 



Opegrapha saxatilis, DC. Flor. Fran^. 2. 312(1805); Chev. Hist, des 



Graphide'es, 56. t. 12. figs. 1, 2, 3; Fries, L. Reform. 366; Hook. Br. 



Fl. 2. 145 (in part) ; Tavl. Fl. Hib. pt. 2. 106 (in part) ; », Massalongo, 



Comm. Lich. 102. t. 19. fig. 120. 



calcarea. Turn. E. Bot. 1/90 (180/). 



calcaria, Ach. L. Univ. 250 (1810); Syn. 72. 



lithyrga, Ach. SjTi. 72. ex specim. Schleicheri in herb. Borrer ! ; Moug. 



& Nestl. Stirpes", ^'b^ ! 



cymbiformis, f. hebraica, B. saxicola, Schaer. Spicil. 331 (1823-1836), 



varia, 6. calcaria, Schaer. Enum. 158 (1851). 



Netley Abbey ! Mr. Lyell in herb. Borrer (on chalk and on 

 mortar). Stone Farm Rocks in Ardingley, Sussex ! Mr. Borrer 

 (on white sandstone). Killarney (on the same stone ^vith O. 

 Chevallieri) ! Miss Hutchins in herb. Borrer. Laraphey, Pembroke- 

 shire ! Rev. T. Salwey. Bangor, Co. Down ! JFm. Thompson, Esq. 

 Newton Wood, Cleveland, Yorkshire ! Mr. J. G. Baker. Great 

 Ayton, Yorkshire ! Mr. G. Dixon. Great Orme's Head, Caer- 

 nanonshire. 



Thallus white, pulverulent, chalky, variable in thickness, 

 sometimes entirely obliterated. Lirell<B scattered or confluent 

 and crowded, peculiarly rigid in general appearance, full-black 

 in colour, straight or slightly cm*ved and nearly hnear in an 

 early state, slightly tapering towards each extremity ; in a later 

 and mature state the disk expands in width in the middle, and 

 the lirellse in consequence become naiTOwly oblongo-elhptical, 

 very markedly pointed or tapered at the extremities, frequently 

 in stellate groups, at other times with a single ray going ofl" from 

 another at nearly a right angle, sometimes two rays so as to form 

 a trifid lirella, sometimes as represented by Chevallier and in 

 ' E. Bot.' with three or four rays, sessile and prominent. The 

 disk in the early state of the lirella is a straight chink or sht, 

 nearly equal throughout its entire length, and the mai-gins tumid 

 and rounded. Subsequently the disk expands in width in the 

 centre, pushing the margins outwards, which become thin, ele- 

 vated and somewhat sharp, bulged or baggy, as would arise if 

 growth had been arrested at the extremities, and still gone on 

 in both directions in the middle of the lirella. Finally, the disk 

 becomes still more elevated and expanded, occupying the whole 

 upper surface of the hrella on a level with the margins, which 



