Twenty species and one variety of the genus Bactrospora Massal. are revised. The following new species are described: B. arthonioides sp. nov., B. brodoi sp. nov., B. carneopallida sp. nov., B. incana sp. nov., B. intermedia sp. nov., and B. spiralis sp. nov. Six species of Lecanactis and one of Bacidia are transferred to Bactrospora. A key is given.

The little known Porina schizospora Vainio is transferred to the genus Strigula as Strigula mediterranea Etayo nom. nov. Strigula mediterranea differs from S. taylorii only in its conidia and its Mediterranean distribution.

Four new species of Caloplaca are described from Antarctica: C. buelliae is parasitic on Buellia, C. iomma has a characteristic deep reddish orange colour on the apothecia, C. psoromatis is parasitic on Psoroma and Pannaria, and C. siphonospora is a parasitic species of mosses, very similar to C. nivalis, but with much shorter spores.

Thelidium austroatlanticum sp. nov. is described from Signy island; it is characterized by an epilithic thallus, more or less appressed involucrellum, and 1-septate spores 30–40 μm long. Thelidium incavatum is also reported for Signy Island.

The new species Peltula sonorensis is described from the Sonoran Desert. It is found in several localities throughout the Mexican part of the Sonoran Desert and belongs to a distinct group within the genus Peltula, which is characterized by fairly large (up to 15 mm diam.), umbilicate-peltate squamules, growing individually and having ellipsoid to bacilliform spores.

The weathering phenomena resulting from the growth of six foliose and crustose lichens (Parmelia subrudecta, Xanthoria ectaneoides, Parmelia conspersa, Aspicilia radiosa, Caloplaca sp. and Ochrolechia parella) on three mafic rocks have been studied. The bioweathering results in more or less extensive fragmentation and corrosion of the mineral surfaces immediately beneath the lichen thalli and in the formation, in the thallus or at the rock-lichen interface, of secondary products. The significant amounts of whewellite found in all interfaces, and the bipiramids of weddellite detected at the serpentine rock-Ochrolechia parella interface, suggest that the oxalic acid secreted by the mycobiont is the chemical substance principally involved. The capacity of the lichens to alter their rock substrata does not appear to be related to their thallus morphology.