Description: Thallus crustose, episubstratic, 0.3-1 mm thick, smooth to slightly rugose-verrucolose, white-grey, pruinose. Cortex 40-60 µm thick, of anticlinally arranged, colourless hyphae immersed in a pale yellow-brown gelatinous matrix; medulla chalk-like throughout. Apothecia lecanorine, stromatoid-pluricarpocentral, numerous, sessile, circular in outline, not constricted at base, 3-8 mm across, with a black but usually white-grey-pruinose disc and an entire thalline margin. Proper exciple inconspicuous; epithecium brownish; hymenium colourless; paraphysoids unbranched or sparsely branched, 1-2 µm thick, the apices 1-3 µm wide; hypothecium black. Asci 8-spored, clavate, bitunicate, the apex thickened with a small internal K/I+ blue ring. Ascospores 3-septate, hyaline, fusiform, 19-23 x 5-6 µm. Pycnidia black,immersed or slightly projecting. Conidia thread-like, sickle-shaped. Photobiont trentepohlioid. Spot tests: thallus surface K-, C+ red, KC+ red, P-; medulla and apothecial disc C-. Chemistry: erythrin, lecanoric acid (the latter sometimes absent).
Note: most common along the coasts of Dalmatia and the eastern Mediterranean region, locally abundant along the coast of Puglia. The record from Venezia Giulia (Nimis 1993: 285) is wrong, and refers to the pycnidiate form of D. massiliensis.