Upper surface of the thallus bearing cephalodia 1. P. aphthosa Upper surface of the thallus devoid of cephalodia. Thallus bearing trichomatic hyphae above. Upper surface bearing isidioid branchlets or lobules 2. P. praetextata Upper surface devoid of isidioid branchlets or lobules. Orbicular sorediate areas on the upper surface of the thallus 3. P. sorediata Soredia lacking on the upper surface. Lower surface of the thallus of light color 4. P. canina Lower surface partly or wholly dark 5. P. rufescens Thallus devoid of trichomatic hyphae. Apothecia orbicular and revolute, spores 4- to 8-celled 6. P. polydactyla Apothecia usually transversely oblong, spores 4-celled 7. P. horizontalis 1. Peltigera aphthosa (L.) Willd. Fl. Berol. Prodr. 347. 1787. _Lichen aphthosus_ L. Sp. Pl. 1148. 1753. Thallus closely attached to the substratum at the center, the lobes ascending, 6 to 8 cm. in diameter, smooth and devoid of trichomatic hyphae above, cephalodia more or less rounded and irregularly scattered over the surface (Fig. 3), the lobes broad and rounded with crenate margins, brown above, the lower surface having numerous veins, these forming a dark brown nap at the center, the veins distinct and light toward the margin, dark rhizoids extending from the veins; medulla composed of thick-walled, densely interwoven hyphae, irregularly disposed; apothecia on extended lobules, orbicular and frequently revolute, the disk red-brown, 2 to 5 mm. in diameter, the margin entire or crenulate; hypothecium pale brown; hymenium hyaline to pale brown above; asci cylindrico-clavate; spores acicular, straight, 4- to 6-celled, 47 to 66 mic. long and 4 to 5 mic. wide (Fig. 8, d). Examined from Clark County. Also reported from Champaign County. On earth and often on humus-covered rocks. Rare in Ohio. 2. Peltigera praetextata (Sommerf.) Fink. Proc. Ind. Acad. Sci. 1918: 267. 1918. _Peltigera ulorrhiza praetextata_ Sommerf. Lapp. Suppl. 123. 1826.