A cladistic biogeographic study of the Namanereidinae was under taken to test whether the biogeographic patterns shown by the species can be explained by vicariance, and whether they support the conventional view of Pangaean break-up and a hypothetical Tethys Sea. The Namanereidinae consists of two monophyletic clades, Namalycastis and Namanereis, members of which exhibit similar distribution patterns. If species of Namalycastis and Namanereis share a common history of fragmentation and diversification then their area cladograms should be congruent and congruent with the postulated sequence of geological fragmentation. Congruence between area cladograms and between taxon and area cladograms was assessed using the COMPONENT program (Page, 1993). Results indicate that the biogeographic patterns shown by species of both genera may be explained largely by vicariance. Rather than supporting the conventional view of Pangaean break-up and a hypothetical Tethys Sea, the results are better explained by the expanding earth model (sensu Shields, 1976, 1979) which predicts that during the Jurassic Period the earth was substantially smaller, the Tethys Sea was much reduced (or absent) and the Pacific was essentially closed. The minimum age of the subfamily is thought to be about 200 My.