Thallus: crustose areolate to granulose, scattered, areolate areoles: 0.25-0.5 mm wide, angular to irregular in outline surface: dull black, rough to granulose attachment: by rhizohyphae Apothecia: sessile, zeorine, small, up to 0.5 mm wide, with thin thalline margin; disc: opening early in development, flat, dark red, receding with age; exciple: distinct (already distinct in juvenile apothecia), often visible as a light ring surrounding the apothecial disc, color faintly yellow to golden, composed of interwoven, gelatinized hyphae; epihymenium: brownish red; hymenium: 100-120 micrometer high, hyaline, amyloid; paraphyses: distinctly septate, branched and anastomosing, apical cells thickened (3-5 micrometer) and colored reddish-brown asci: 8-spored ascospores: simple, hyaline, broadly ellipsoid to ellipsoid, (10-) 12.5-17.5 (-22.5) x (7.5-) 10-12.5 (-15) micrometer; walls: thin Pycnidia: immersed, globose, 0.1-0.125 mm wide, simple; wall: convoluted with age conidia: ellipsoid, 3-4 x 1.5 micrometer Spot tests: all negative Secondary products: none detected. Substrate and ecology: on caliche crusts, limestone and rhyolite, and on small pebbles in washes; in sheltered or rather exposed habitats; montane World distribution: Europe and SW North America Sonoran distribution: south-central Arizona. Notes: the species is extremely similar to Psorotichia and Porocyphus, but they lack L. arnoldianas characteristic yellowish to golden color of the entire excipulum. Porocyphus also has a distinct exciple that is sometimes yellowish brown colored, but only in the uppermost parts; it mainly differs from Lemmopsis in its type of ascoma development (pycnoascoma) and its slender paraphyses. Furthermore, if Psorotichia has an exciple, then it lacks coloration and is very thin. Also the subhymenium of Psorotichia usually extends as a stipe deep into the thallus (not found in Lemmopsis).