The Dahomey Gap as evidenced by land molluscs, a preliminary report resulting from a reconnaissance of the literature

A survey of the pertinent literature has shown that the Dahomey Gap, a major interval in the West African forest block, is indeed a significant biogeographical barrier for land molluscs. The West African forest has been reduced to four refugia 18,000 years BP, subsequently merging into the western (Upper Guinea) and eastern (Lower Guinea) divisions of this forest belt. This vicariance event must have considerably influenced the distribution of terrestrial gastropods. From the literature it appears that insufficient data are yet available to draw conclusions. Our knowledge of the phylogeny (particularly sister-group relationships) of most groups is still in its infancy, although there are strong indications that much of the local endemism has originated in the four refugia.