Thallus usually verrucose, areolate or subareolate, tending toward squamulose conditions, better developed than in other members of the family, scarcely ever showing granulate conditions, and never disappearing entirely; apothecia also larger than in the other genera, adnate to immersed, usually black, but rarely white-pruinose; hypothecium usually dark brown; hymenium pale to light brown; spores 4-celled to muriform, and pale to brown, various conditions of septation and coloration sometimes appearing in the same hymenium. KEY TO THE SPECIES OF RHIZOCARPON On bark 2. R. _alboatrum_ On rocks. Spores smaller and 4-celled 1. R. _vernicomoideum_ Spores larger and becoming muriform 3. R. _petraeum_ 1. Rhizocarpon vernicomoideum sp. nov. Thallus of minute, rounded, scattered or sometimes clustered, straw-colored granules, covering small areas, and usually resting on and limited wholly or in part by a black hypothallus; apothecia minute to small, 0.2 to 0.6 mm. in diameter, black, semi-immersed to adnate, at first flat with a thin somewhat raised exciple, becoming convex with the exciple finally covered; hypothecium brown; hymenium pale or tinged brown below and light brown above; paraphyses coherent, distinct or semi-distinct; asci clavate; spores brown, 4-celled, becoming slightly constricted at the septa, 15 to 18 mic. long and 5 to 7 mic. wide, 8 in each ascus. Collected at Cantwell Cave in Hocking County. On shaded sandstone, intermingled with an ash-gray, crustose thallus, which appeared like a sterile _Pertusaria_. The type specimen is deposited in the writer's herbarium, and a cotype may be seen in the State Herbarium. The plant resembles _Buellia vernicoma_ Tuck. 2. Rhizocarpon 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.