Three new species of Diploicia are described from the Galapagos Islands and a fourth, D. glebosa, is transferred from Pyxine; all four are considered endemic to the archipelago. In order to accommodate these species, the generic concept of Diploicia has been emended. Two of the species are sterile; D. leproidica is placodioid-leproid, where the thalli derive from pseudocorticate granules aggregating into small, placodioid rosettes with distinctly lobate margins. The second sterile species, D. squamulosa, forms scattered squamules that eventually aggregate into small, placodioid rosettes. The two fertile species, D. glebosa, with an olivaceous to beige, smooth, epruinose upper surface, and D. neotropica, with a white to grey-white, roughened, pruinose upper surface, form larger thalli typical of Diploicia, have apothecia that are initially lecideine, but are soon engulfed and hidden by a thick thalline margin. Anatomically the proper exciple remains visible for a considerable part of the ontogeny, although it eventually becomes almost completely reduced to a few pigmented or almost hyaline hyphae. This transition from lecideine to lecanorine apothecia is similar to the physciaeformis-type ontogeny observed in some Pyxine species. Several species currently accommodated in Buellia s. lat. with diploicin and effigurate thalli that lack distinctly lobate margins are discussed and the Socotran endemic Physcia endopyxinea is transferred into Diploicia.