Thallus: crustose but sometimes slightly bullate or nearly subfruticose, effuse, 0.2-1.1 mm wide surface: varying from creamy white to grayish white, smooth, slightly pruinose soredia: often present, granular, when young in punctiform soralia that becoming maculiform to capitate when old cortex: 35-65 µm thick Ascomata: numerous, circular in outline, sessile, 0.5-2 mm diam.; exciple: usually undulating or strongly undulating sometimes to the extent that the ascomata may become stromatoid; hymenium: 50-140 µm high; paraphysoids: sparsely branched, parallel, hyaline, c. 1 µm in diam. asci: clavate, 70-120 x 15 µm, 8-spored ascospores: fusiform, hyaline, 3-septate, 23-29 x 5-6 µm Spot tests: cortex K-, C+ red, KC+ red, P-; medulla K-, C+ red, KC+ red, P- Secondary metabolites: erythrin, lecanoric acid, and an unknown substance. Substrate and ecology: growing on vertical or overhang rocks and cliffs near the sea; occasionally abundant with individuals forming large mosaic patterns World and Sonoran distribution: along the Californian coast from Monterey Co. in the north to Baja California Sur. The two forms, Dirina cataliariae f. catalinariae and D. catalinariae f. sorediata are sympatric throughout their respective ranges.