10 BRITISH LICHENS: 
66. Urceolaria Ach. Thallus crustaceous, continuous or areolate : 
apothecia urceolato-impressed, with a proper and a thalline margin, 
and spores septately murali-divided ; spermogones with somewhat 
branched sterigmata and cylindrical spermatia. 
Subtribe V. LECIDEEI Nyl. Thallus variously ‘ crustaceous, 
pulverulent, or none proper; gonidial layer consisting of gonidia 
(rarely of chrysogonidia): apothecia patéllulate. 
67. Lecidea Ach. Thallus squamose, areolate, pulverulent, or 
none proper: apothecia biatorine, gyalectoid, or lecideine, with 
simple or variously septate spores; spermogones with simple or 
simplish sterigmata and acicular, straight or arcuate, or shortly 
cylindrical spermatia. 
68. Odontotrema Nyl. Thallus macular, indistinct: apothecia 
thelotremoideo-lecideine or gymnotremoid, with simple or thinly 
3-septate spores ; spermogones not observed. 
Tribe XIX. GRAPHIDEI Nyl. Thallus crustaceous, thin, con- 
tinuous, often but little visible, rarely wanting ; gonidial layer con- 
sisting of gonidia: apothecia lirelline or rotundate. 
69. Xylographa Fr. Thallus maculate, hypophleodal : apothecia 
lirelline or oblong, with simple spores; spermogones with simple 
sterigmata and acicular curved spermatia. = 
70. Agyrium Fr. Thallus maculate, scarcely visible: apothecia 
oblong or rotundate, with simple spores; spermogones not known. 
71. Lithographa Nyl. Thallus crustaceous or evanescent: apo- 
thecia lirelline, with simple spores ; spermogones not yet seen, 
72. Opegrapha Humb. Thallus usually hypophlcodal or obsolete : 
apothecia lineari-lanceolate, subrotundate or linear, with 1- or 
multi-septate spores; spermogones with simple sterigmata, and 
cylindrical, straight or arcuate spermatia. 
73, Platygrapha Nyl. Thallus thin or obsolete: apothecia 
plane, simple, with spurious thalline margin and septate spores; 
spermogones with simple sterigmata, and’ cylindrical, straight or 
slightly curved spermatia. 
74, Stigmatidium Mey. Thallus distinct, crustaceous, thickish : 
apothecia punctiform or elongate, with variously septate spores; 
spermogones with simple sterigmata and short straight spermatia. 
75. Arthonia Ach. Thallus thin, or hypophlceodal and eva- 
nescent, rarely wanting, internally sometimes with chrysogonidia : 
apothecia roundish or difform, plane or tumid, with variously 
septate spores; spermogones with simple sterigmata, and cylindrical, 
straight or curved spermatia. 
