Thallus: crustose to subsquamulose or squamulose; prothallus: not discernible areoles: flat to squamulose, 0.5-1.4 mm in diam., round to irregular in outline surface: ochre to light brown, with a thin white, smooth, faintly glossy, with a rough margin, esorediate cortex: C- medulla: white, I-, K-, C- Apothecia: black, with a slightly constricted base, occurring between or marginally at the areoles, up to 2.3 mm in diam., 40-150 per mm2 disc: black, flat to slightly convex margin: black, usually small, regular, persistent, dull to shiny exciple: blackish brown peripherally, shifting to (faintly) reddish brown in K, interior part pale brown (may appear dark brown in hand sections), 40-80 µm wide epihymenium: dull green (cinereorufagreen), 10-20 µm thick hymenium: hyaline, 50-75 µm tall, I+ blue (in this herbarium specimens!); paraphyses: simple, but relatively often branched and anastomosing subhymenium: unpigmented, 12-25 µm thick hypothecium: dark brown to almost black, 100-200 µm thick asci: clavate, 50-70 x 13-17 µm, 8-spored ascospores: hyaline, simple, ellipsoid, 10-17 x 4.5-7.5 µm, length-width-index: 2-2.4 Pycnidia: immersed conidia: cylindrical, 8-16 x 1-1.3 µm [studied in 1 specimen] Spot tests: cortex and medulla K-, C-, KC-, P- Secondary metabolites: confluentic acid, and/or 2'-O-methylperlatolic acid. Substrate and ecology: on acid rock from lower montane to montane zones World distribution: western North America in coastal mountain ranges from Washington to California Sonoran distribution: not yet known, but to expected. Notes: Lecidea fuscoatrina resembles Lecidea atrobrunnea in the field. Its morphological characters however (I- medulla, blackish brown hypothecium, larger ascospores) are those of Lecidea fuscoatra, from which it differs mainly chemically, having confluentic acid syndrome instead of the gyrophoric acid syndrome. Lecidea fuscoatrina is closely related to Lecidea santessonii Hertel (only known from Patagonia), which differs in having slender-oblong, thinner ascospores (8-13 x 2.5-5 µm (length width index: 2.8-3.2: 1). Although Lecidea fuscoatrina is not yet known from the Sonoran area, it is included here because it should eventually be found.