Thallus adnate, rather closely attached to the substratum by numerous short, hyaline, thick-walled rhizoids, irregular or sometimes orbicular in form, 6 to 10 cm. in diameter, green-gray to brown above, smooth or bearing tooth-like branchlets, narrowly and laciniately lobed, the margins of the lobes serrate or crenate, slightly ascending, beneath finally tomentose, and brown or black-brown; plectenchymatous cortices well developed above and below; medulla of narrow, thin-walled, densely, variously disposed hyphae; apothecia numerous, the disk red-brown to almost black, 1.3 to 3 mm. in diameter; hypothecium of interwoven hyphae, pale brown; hymenium pale brown below and darker above; asci clavate; paraphyses simple or branched, slightly swollen and brown at the apex; spores brown, ellipsoid, 4-celled, 15 to 21 mic. long and 5.5 to 8 mic. wide. Examined from Butler and Champaign Counties. On trunks and mossy rocks. Rare and usually sterile in Ohio. EXPLANATION OF PLATE XIV Fig. 1. A section through the thallus of _Peltigera canina_, showing the cortex above and the medulla below, the medullary hyphae of the lower portion running in a somewhat horizontal direction. The algal cells shaded. X 380. Fig. 2. A section through the thallus of _Nephroma helvetica_, showing the cortices, upper and lower, and the mycelial medulla within. The algal cell shaded. X 760. Fig. 3. A section through a cephalodium of _Peltigera aphthosa_; a, the surrounding cortex; b, the internal hyphae and the cells of the algal host; c, the supporting hyphae from the thallus below. Partly diagramatic. X 48. Fig. 4. A small portion of a section through the exciple of _Peltigera canina_, showing the plectenchymatous structure. X 380. [Illustration: PLATE XIV.] EXPLANATION OF PLATE XV Fig. 5. A section through the cortex of _Peltigera canina_, showing its relation to the medullary hyphae. X 760. Fig. 6. A portion of a section of the hymenium of _Peltigera canina_, showing two asci containing spores, two asci with protoplasmic contents, and five paraphyses. X 760. Fig. 7. A portion of a section through an apothecium of _Peltigera canina_, showing part of the hymenium of interwoven hyphae below and the bases of three paraphyses above. X 760. Fig. 8. Types of spores found in the _Peltigeraceae_: a, 4-celled spores of _Peltigera horizontalis_; b, 6- to 8-celled spores of _Peltigera sorediata_; c, 4-celled spores of _Peltigera aphthosa_; d, 4- to 8-celled spores of _Peltigera canina_. X 380. The drawings were made with camera lucida and were reduced one-half in making the plates. [Illustration: PLATE XV.] INDEX Bacidia, 345 Bacidia egenuloidea, 346 Bacidia fuscorubella, 346 Bacidia incompta, 347 Bacidia inundata, 347 Bacidia rubella, 346 Bacidia schweinitzii, 347 Bacidia umbrina, 348 Biatorella, 336 Biatorella pruinosa, 337 Biatorella simplex, 336 Biatorina, 341 Biatorina chalybeia, 341 Biatorina heerii, 343