The endemic Macaronesian Canaridiscus, provisionally placed in the Discidae genus Atlantica, are closely linked to the peculiar laurel forest habitat of these islands. Knowledge of Atlantica (Canaridiscus) is increased here with the description, for the first time, of the genital system of three more of its species. The epiphallus is apparently lacking and the penis is much longer than that known from any of the Discidae of Europe and North America; generally it is too large to be more than partly accommodated in the distal female genital tract. Keraea has been regarded as an endemic Macaronesian genus of Discidae known only from a few shells, but its Madeiran species has been identified as a Trochulus (Hygromiidae) and its type species (from Tenerzfe) also matches Hygromiidae, not Discidae.
The origin and relationships of the Macaronesian Discidae are discussed. The simplest explanatory model is apparently that they represent the last living relicts of a more diverse fauna of Discidae that lived in Europe during the Tertiary; Atlantica (Canaridiscus) was probably isolated early on from the remaining Discidae. Recent literature reports multiple patterns of colonisation of Madeira and the Canaries that have varied between different groups of plants and animals. Hence, it is argued that it is unwarranted to expect to find only the single pattern of colonisation among the land snails of each of these archipelagos that was advocated by Waldén (1984).