Halidesmus socotraensis is described from six specimens, 39.6-69.5 mm SL, from the Socotra Archipelago, western Indian Ocean. It is distinguished from all other congrogadine species in having the following combination of characters: three lateral lines (dorsal, middle and ventral complexes); ventral lateral line branched on abdomen, with unpaired median section on ventral midline; and upper lateral line without anterodorsal branch on to nape. Haliophis guttatus is also newly recorded from the Socotra Archipelago on the basis of 15 specimens.