Four species of the Talitridae, Trinorchestia longiramus n.sp., Platorchestia crassicornis (Derzhavin, 1937), P. munmui n.sp., and P. pachypus (Derzhavin, 1937) are described from the sandy or gravelly coasts of Korea, and their distribution is mapped. The taxonomic distinction between two confused species P. crassicornis and P. platensis (Kreyer, 1845) is restudied by comparison with material from northwestern Pacific and Atlantic coasts, some significant characters of the latter are illustrated, and the doubtful distribution of the latter in the Indo-Pacific region is discussed to some extent. A scanning electron microscope study reveals that the microstructure of the retinacula might be useful for the taxonomy of the group.