188 LECANO-LECIDEEI [rHIZOCARPON 



black, almost plane, umbonate or usually somewhat plicate or 

 wrinkled, the margin thin, flexuose ; hypothecium black ; para- 

 physes slender, bluish-green or dark-brown towards the tips; 

 spores oblong, colourless or rarely brownish, 3-septate, slight, 

 constricted at the septa, sometimes halonate, 0,018-24 mm. 

 long, 0,008—11 mm. thick; hymenial gelatine bluish with iodine. 

 — Bh. petrseum var. (Ederi Mudd Man. p. 220 (1861). Lichen 

 (Ederi Web. Spicil. Fl. Goett. p. 182 (1778) (non Engl. Bot.). 

 Lecidea CEderi Ach. Meth. p. 49 (1803); Leight. Lich. Fl. 

 p. 329 ; ed. 3, p. 349. L. petrsea subsp. CEderi Cromb. Idch. 

 Brit, p: 87. 



Exsicc. Leight. n. 187; Larb. Lich. Hb. n. 179. 



Often confused with Lecanora Diclisonii (see Part I. p. 476) on 

 account of the rusty-red colour of the thallus. 



Hob. On maritime and mountainous rocks. — Distr. Not un- 

 common throughout Great Britain and Ireland ; not recorded from 

 the Channel Islands. — B. M. Xear Launceston, Cornwall ; Barmouth 

 and DolgeUy, Merioneth ; Trefriw, Camarvonshue ; Lounsdale, Cleve- 

 land, Yorkshire ; King's Park, near Edinburgh ; Nigg, Kincardine- 

 shire ; Ben Vrackie and Ben Lawers, Perthshire ; Appin, Argyll ; 

 Glen Gallater, Glen Ey and Castleton, Braemar, Aberdeenshire ; Glen 

 Nevis, Invernessshire ; BaUinakiel, Connemai-a, Galway. 



3. Rh. alboatrum Th. Ft. Lich. Arct. p. 237 (I860).— 

 Thallus effuse, whitish or greyish, somewhat areolate or granular 

 or almost disappearing (K — , CaCl — ); hypothallus wanting. 

 Apothecia small, black, sometimes whitish-pruinose, adnate, 

 convex, sometimes with a spurious white margin ; hypothecium 

 dark-brown; paraphyses slender, capitate and dark- brown at 

 the tips; spores ellipsoid, brown, 1- or 3-septate or ii-regularly 

 muriform, not halonate, 0,016-20 mm. long, 0,007-9 mm. thick ; 

 hymenial gelatine deep-blue with iodine. — Lichen alboater Hoffin. 

 Enum. Lich. p. 30 (1784). L. corticola Ach. in Vet. Acad. 

 Handl. 1795, p. 137, t. 5, f . 6 ; Dicks. PI. Crypt, iv. p. 20 

 (1801) ; Engl. Bot. t. 1892. Lecidea corticola Ach. Meth. p. 53 

 (1803); S. F. Gray Nat. Arr. i. p. 469 (1821) pro parte. 

 Pateltaria leucoplaca DC. Fl. Franc, v. p. 347 (1805) ? L. alboatra 

 Fr. Lich. Eur. p. 336 (1831) ; Hook, in Sm. Engl. Fl. v. p. 180; 

 Cromb. Lich. Brit. p. 87 (inch var. leucoplaca) ; Leight. Lich. Fl. 

 p. 326 (inch f. leucoplaca) ; ed. 3, p. 346 (incl. f. populorum). 

 Diplotomma alboatrum Flot. ex Massal. Ric. Lich. p 98 (1852) ; 

 Mudd Man. p. 218, t. 4, f. 82 (incl. vars. trahellinum and 

 populorum). 



Exsicc. Leight. n. 64 ; Mudd nos. 188 (as Buellia disciformis 

 var. rugulosa), 191, 192 (var. populorum) ; Larb. Lich. Hb. 

 n. 176 ; Johns, n. 396. 



A number of forms have been distinguished according to differences 

 noted in the appearance of the thaUus or apothecia. Var. trahinella 

 (Lecidea alboatra var. trahinella Fr. I. c.) represents a somewhat 

 warted form of thallus with the apothecia, crowded, often confluent 



