100 CONTRIBUTIONS FROM THE NATIONAL HERBARIUM. 
3. Rhizocarpon caleareum concentricum (Dav.) Th. Fr. Lich. Scand. 2: 632. 
1874. PuaTE 8, A. 
Lichen concentricus Dav. Trans. Linn. Soc. Lond. 2: 284. 1794, 
Thallus white or whitish, smoothish or becoming chinky and finally areolate with 
quite minute areoles, in ours frequently disposed in more or less circular areas upon 
the substratum, the areas not more than 3 to 5 cm. in diameter; apothecia frequently 
showing a well-defined concentric arrangement, said to be 1 to 1.5 mm. in diameter, 
but only 0.3 to 1 mm. in ours of this subspecies, immersed or adnate, the disk flat and 
dull black or dark brown, rarely whitish-pruinose, the exciple dull black and per- 
sistent; hypothecium dark brown; hymenium pale below and brownish above; para- 
physes coherent or becoming distinct, simple or branched, thickened and brownish 
toward the apex; asci clavate or inflated-clavate; spores hyaline or brown, muriform 
in ours, said to be at first 4-celled, 22 to 39 « long and 11 to 16 » wide. 
The suborbicular thallus and the concentric arrangement of the apothecia are the 
special marks of the subspecies and to this may be added that the disk is said to be 
sometimes concave. 
Collected at Rainy Lake City and at Kettle Falls. On rocks. Also at Grand 
Marais, and not previously reported from this locality, where the likeness given here- 
with was secured. 
Not known elsewhere in North America. Found also in Europe. 
The material from Grand Marais, determined by T. Hedlund, is plainly marked, and 
distinct from any form of Rhizocarpon petraewm, but I am disposed to think that all the 
forms recorded in the preliminary reports as Buellia concentrica belong to that species. 
EXPLANATION OF PLATE 8.—A, Plant of Rhizocarpon calcareum concentricum on rocks, showing the 
orbicular crustose thallus and the concentrically arranged apothecia. B, Plant of R. geographicum on 
rock, showing the areolate crustose thallus and the immersed apothecia. A enlarged 2} and B 3 diameters, 
4. Rhizocarpon ignobile Th. Fr. Lich. Scand. 2: 619. 1874. 
Thallus ashy or ashy brownish, chinky or minutely verrucose-areolate, continuous 
or scattered upon the black hypothallus, more or less circular in small areas or more 
widely and irregularly distributed over the substratum; apothecia commonly im- 
mersed, small or minute, 0.3 to 0.7 mm. in diameter, the disk dull black, flat or 
becoming convex, the exciple black and frequently disappearing; hypothecium dark 
brown; hymenium pale, or pale below and brownish above; paraphyses frequently 
cohering, simple or branched, commonly enlarged and brownish toward the apex; 
asci clavate or inflated-clavate; spores in ours most frequently 2-celled, but passing 
into 4-celled and rarely into muriform conditions, hyaline, 14 to 20 » long and 6 to 
11 » wide. 
Determined by A. Zahlbruckner from Grand Portage Island and not previously 
reported from Minnesota. On rocks. Also, the plant from Rainy Lake City recorded 
as Buellia concreta in the last preliminary report seems to belong here. This was 
also determined by Doctor Zahlbruckner. 
Rhizocarpon concretum is known from Newfoundland, but R. ignobile has not been 
previously reported from North America. Found also in Europe. 
5. Rhizocarpon geographicum (1.) Lam. & DC. FI. Fr. ed. 3. 2: 365. 1805. 
Puate 8, B. 
Lichen geographicus L. Sp. Pl. 1607. 1753. 
Thallus, greenish to bright yellow upon a black hypothallus, composed of small 
areoles scattered over the substratum upon the conspicuous hypothallus or crowded 
into a continuous crust, in the latter case sometimes verrucose or chinky rather than dis- 
tinctly areolate, the areas upon the substratum often quite small; apothecia small, 0.4 
to 1 mm. in diameter, often crowded together in groups, and then angulate, in the more 
continuous forms of thalli immersed between the areoles or in the thallus, the disk 
black and flat or convex, the exciple black and somewhat prominent, but often dis- 
appearing; hypothecium dark brown; hymenium pale, or pale below and brownish 
