Thallus: rimose-areolate, 0.2-0.4 mm thick, without a black basal layer (but medulla partly brown) areoles: angular, plane to somewhat tumid, 0.3-0.6 mm wide, incompletely subdivided by cracks surface: brown, smooth to slightly rough anatomy: upper cortex: hyaline, 10-20 µm thick, composed of cells 4-6 µm diam., overlain by a thin hyaline epinecral layer; algal layer: 50-100 µm thick, with algal cells 6-10 µm in diam., mycobiont portion: paraplectenchymatous; alga-free medulla: subparaplectenchymatous, with a colorless upper part and ±brown lower zone obscured by substrate particles and crystals Perithecia: 1-3 per areole, remaining immersed in raised portions of the areoles and largely covered by thallus tissue, only the very tips exposed; exciple: subglobose, 0.3-0.4 mm wide, 20-25 µm thick, brown to brown-black; involucrellum: extending (almost) to the base-level of the exciple or somewhat incurved beneath, laterally 40-80 µm thick, slightly thinning toward the base, arching slightly away from the exciple, the space between involucrellum and exciple pale and packed with crystals; periphyses 35-50 µm long, 2.5-4 µm thick, branched-anastomosing asci: clavate, 60-70 x 20-25 µm, 8-spored ascospores: hyaline, simple, ellipsoid or oblong-ovoid, 20-25 x 9-12 µm Pycnidia: unknown Spot tests: all negative Secondary metabolites: none detected. Substrate and ecology: epilithic, on calcareous or superficially calciferous rocks World distribution: formerly known only from France Sonoran distribution: one record from Sonora. Notes: The structure of the involucrellum is distinctive. In Verrucaria papillosa the involucrellum may be similarly developed, but the thallus is inconspicuous, and the spores are larger.