212 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
KEY TO THE SPECIES. 
Section I. Thallus more or less lobed at the circumference. 
Thallus large, 25 to 70 mm. in diameter................... 1. 
Thallus smaller. 
Thallus only 8 to 45 mm. in diameter................. 2. 
Thallus still smaller... ..2.2222020.00.20......-...... 2a. 
Section I]. Thallus not lobed at the circumference. 
On trees or on dead wood. 
On dead wood. 
Thallus dirty yellow or orange, of adnate squamules, 
often forming an areolate crust................. 4. 
Thallus ashy or whitish. 
Thallus persistent and becoming thick and 
verrucose. 2.2.2... le. 9, 
Thallus thinner and tending to disappear. 
Disk yellowish orange; exciple disappear- 
Disk olivaceous and darker; exciple dis- . 
appearing........0.000 00000220 20.00000. 9a. 
On trees. 
Thallus chinky, verrucose or areolate, grayish yel- 
low or yellowish gray (also on rocks and old 
wood)... 22.22. eee ee ee 6. 
Thallus thinner and smoother, often chinky, ashy- 
whitish or lead-gray. 
Exciple entire........222000000.00..2.2..2.. 7 
Exciple becoming subcrenulate or radiately 
striate; disk pruinose..........2.220...... 7a. 
On rocks. 
Thallus thick and often verrucose. 
Thallus grayish yellow or yellowish gray; disk 
orange to saffron-colored......2......0..0..... 6. 
Thallus sea-green to iron-gray; disk yellowish rust- 
colored to blackish... ....22220002.02...00.... 7b. 
Thallus thinner, granulose, chinky, or areolate, 
Thallus chinky-areolate or scattered-scaly, the 
scales often lobed; usually dark orange.......... 3. 
Thallus granulose to areolate. 
Granules minute, lemon-colored, sometimes 
compacted into a subareolate crust... .. 2... 5. 
Granules larger and often crenate-lobed, bright 
greenish yellow (also on old wood). 
Thallus persistent, the granules often com- 
pacted into an areolate crust; exciple 
granulate, crenate... 2.222.002.2222... 10. 
Thallus of scattered granules, often disap- 
pearing; exciple entire................ 10a. 
P. elegans. 
P. murorum., 
P.murorum — mini- 
atum. 
P, microphyllinum. 
P. ferrugineum. 
P. pyraceum, 
P. ferrugineum polli- 
nit, 
P, aurantiacum. 
. P. cerinum. 
~ 
P. cerinum ulmorum. 
P. aurantiacum. 
P. cerinum sideritis, 
P. cinnabarrinum. 
P. ettrinum. 
P., vitellinum. 
P. vitellinum  aurel- 
lum. 
