Thelidium declivum

Description. Prothallus not visible. Thallus white, grey or pale brown, endolithic to rarely thinly epilithic, algal cells c. 5 - 8 μm, in one specimen (type) surrounded by dark lines. Perithecia 0.12 - 0.44 mm in diam., 1 / 2 - 1 - immersed, often surrounded by thalline collar, leaving shallow to usually deep pits; c. 20 - 80 perithecia / cm 2. Ostiole pale to dark, plane to depressed, c. 20 - 50 μm wide. Involucrellum absent, apical or covering half of the exciple, 0 - 70 μm thick, appressed to the exciple or clearly diverging from it. Exciple 0.22 - 0.38 mm, wall dark brown to black, c. 25 - 40 μm thick, apex may be thickened to 50 - 70 μm thick. Periphysoids c. 30 - 50 x 1.5 - 2.5 μm. Asci c. 91 - 132 x 31 - 48 μm, 8 - spored. Ascospores (1 - 2 -) 3 - septate, few spores submuriform with 5 - 6 (- 8) cells, (32.3 -) 35.3 - 37.8 - 40.4 (- 44.4) x (12.6 -) 14.0 - 15.0 - 16.1 (- 17.3) μm (n = 69).