56 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
1. Rhizocarpon geographicum (L.) Lam. & DC. 
Thallus yellow and greenish yellow, areolate, the areoles flat, contiguous (forma 
contigua Fries) or dispersed, with a distinct hypothallus; apothecia small, scarcely 
exceeding 0.5 mm. in width, impressed, the disk black, mostly angular, the margin 
black, thin; apothecia numerous, often crowded, interspersed among the areoles (the 
typical form) or encircled by an areole (forma lecanorina Floerke); epithecium con- 
tinuous, light yellowish brown; thecium about 160 s# high, colorless or of a pale yellow- 
ish brown tint; paraphyses stout, 2 to 4 thick, their oujlines not clean cut, containing 
many guttule; hypothecium dark brown, gradually paling upward; asci ventricose; 
spores variously shaped, short-ellipsoid or oblong, 4-locular but mainly muriform, dark 
brown, the loculi with a bluish black tint, mostly with 3 main septa and additional 
secondary, thinner partitions, 30 to 40 4 long, 14 to 20 # thick; hymenial gelatine blue 
with iodine. 
On hard crystalline rocks. Santa Cruz Mountains at 928 meters altitude, Herre; 
in the mountains of southern California at about 1,000 meters and ascending thence. 
From the central part of North America to arctic regions; Europe. The forms occur 
together and with the type. 
2. Rhizocarpon viridiatrum (Floerke) Koerb. 
Thallus greenish yellow, areolate, the areoles distinctly verruculose, pulverulent; 
hypothallus black; apothecia arising from the black hypothallus, subsessile, pro- 
truding above the level of the thallus and somewhat larger than in the preceding 
species, the disk dull black, flat to convex, papillate or roughened, the margin some- 
what brown black, crenulate, long-persistent; spores as in R. geographicum. 
On trap rock, Topanga Canyon, Santa Monica Range. Europe. 
The thallus does not spread so wide as in R. geographicum and appears dusky from 
fine capillary lines extending over the areoles. 
3. Rhizocarpon geminatum (F lot.) Koerb. 
Crust verrucose-areolate, dark ash gray with a faint shade of red or brown, scattered 
or approximate; hypothallus not very distinct; apothecia sessile; disk flat, black, the 
margin slightly elevated, entire, and persistent; epithecium granulose, violaceous 
black; thecium pallid; paraphyses coherent; hypothecium black brown; asci ven- 
tricose; spores one or two in the asci, 28 to 36 # long, 16 to 20 fe thick, dark brown; 
hymenial gelatine staining an intense blue with iodine, especially the epithecium, 
this becoming almost black; no change with NO,. 
On rocks. Santa Cruz Mountains, Herre; San Bernardino Mountains near “Seven 
Oaks” at 2,000 meters altitude. 
4. Rhizocarpon petraeum (Wulf.) Koerb. 
Thallus as in the preceding, not stained by KHO; spores 6 to 8 in the asci, oblong, 
brown, 4 to 5-locular and submuriform with a thick halo, 22 to 32 fe long, 10 to 16 pt 
thick; hymenial gelatine with iodine blue; no change with KHO or NO. 
With the preceding. Throughout the greater part of North America; Europe. 
5. Rhizocarpon distinctum T. Fries. 
Thallus whitish to leaden gray, interruptedly rimose-areolate, the areoles small, 
flattish or concave, KHO—, Ca(Cl0).—; hypothallus black; apothecia adnate, small, 
0.5 to 0.75 mm. wide, the disk dull black, flat, papillate, with a thin, yellowish gray, 
at first slightly elevated margin, later obsolete as the disk becomes convex; epi- 
thecium brown black, gradually paling downward, with KHO pale violaceous; 
thecium pallid, with iodine blue; paraphyses coarse; spores muriform, colorless, 
oblong-ellipsoid, 24 to 36 « long; 12 to 16 p thick. 
On argillaceous sandstone and shale, near Pescadero and near New Almaden, Jerre; 
may extend to southern California. 
