Three species of whirligig beetles occur in the Bismarck archipelago (Gyrinus sericeolimbatus Rég., Macrogyrus ovatus Ochs, and Dineutus neobritannicus Ochs). Nine species occur on the Solomon Islands, viz. G. sericeolimbatus Rég., D. heterandrus Ochs and the following species of Dineutus (Callistodineutus): bougainvilleanus Ochs, bufo n.sp., choiseulicola n.sp., cristobalensis n.sp., dispar Ochs, dispersus n.sp., and pagdeni Ochs. - The morphological spectrum of subgenus Callistodineutus is reviewed and the distribution pattern and the differentiation of the species analysed. Ten species (of 11) are endemic. The general character is Indonesian. The Callistodineutus have spread twice over the islands, resulting in an older eastern group and a younger western. The western species are associated with a former continuous land connection, severed about 10 000 years ago. A stage of secondary dispersal (exchange of species among the islands) is still in progress.