carpon alboatrum (Hoffm.) Th. Fr. Nov. Act. Reg. Soc. Sci. Ups.
III. 3: 337. 1861.

_Lichen alboater_ Hoffm. Lich. Icon. 30. 1784.

Thallus ash-gray varying toward white, commonly spread widely over the
substratum as a continuous or rarely scattered or disappearing, smooth,
chinky, verrucose-areolate, or sometimes mealy crust: apothecia small to
middle-sized, 0.35 to 1 mm. in diameter, adnate or immersed, dull black
and often more or less white-pruinose, flat with the black exciple
visible, or convex when the exciple often becomes covered; hypothecium
brown to black-brown; hymenium pale or tinged brown; paraphyses
distinct, but sometimes coherent; asci clavate; spores oblong-ellipsoid,
brown, 4-celled to muriform, 12 to 22 mic. long and 4 to 9 mic. wide
(Fig. 8), 8 in each ascus.

Collected in Butler, Preble, Ross, and Highland counties. On bark,
especially elm bark. Also reported from Ottawa County. Rare but
doubtless distributed widely in the State.

3. Rhizocarpon petraeum (Wulf.) Koerb. Syst. Lich. 260. 1855.

_Lichen petraeus_ Wulf. in Jacq. Coll. Bot. 3: 4. pl. 6. f. 2a. 1789.

Thallus an ash or green-gray crust, or varying toward brown or
brown-black, smooth to more commonly roughened, chinky to areolate,
continuous or scattered, of moderate thickness, often widely and
irregularly disposed on the substratum; apothecia small to large, 0.5 to
1.3 mm. in diameter, immersed to adnate, black-brown to black, flat with
the concolorous exciple visible, or becoming somewhat convex, with the
exciple often covered; hypothecium dark brown; hymenium pale, or tinged
brown, especially above; paraphyses coherent, semi-distinct; asci
clavate or inflated-clavate; spores oblong-ellipsoid, 4-celled to
muriform, hyaline to finally brown, 15 to 40 mic. long and 7 to 18 mic.
wide. 8 in each ascus (Fig. 9).

Collected in Lake, Hocking, and Ross counties. Also examined from
Summit, Vinton, and Ashtabula counties. On rocks. Rare but widely
distributed in the State.

EXPLANATION OF PLATE XIII

Fig. 1. Five paraphyses of _Rhizocarpon alboatrum_ to illustrate types
of simple and branched forms found in the same hymenium. X 450.

Fig. 2. A section of the thallus of _Bacidia rubella_ and two cells of
the woody substratum: a, the upper densely interwoven portion of the
thallus; b, part of the less densely interwoven portion below; c, the
algal-host cells; d, one of the cells of the woody substratum and three
hypal rhizoids