New polymorphic species of the genus Menimus Sharp, 1876 (Diaperinae Latreille, 1802, Gnathidiini Gebien, 1921, Gnathidiina Gebien, 1921) from Borneo and Sumatra are described: M. burut sp. n., M. crockeri sp. n., M. dasun sp. n., M. dayak sp. n., M. grimmi sp. n., M. jacobsoni sp. n., M. kadazan sp. n., M. kinabalucus sp. n., M. loebli sp. n., M. matangicus sp. n., M. merkli sp. n., M. punggulicus sp. n., M. sabahicus sp. n., M. sarawakicus sp. n. A new synonym is proposed: Menimus seriepunctatus Gebien, 1927 (Menimus malayicus Schawaller, 2016 syn. n.). A lectotype is designated for Menimus seriepunctatus Gebien, 1927. Menimus burut sp. n. and Menimus sabahicus sp. n. are the first known species with 9-segmented antennae, whereas Menimus matangicus sp. n. completely lacks eyes. An identification key is compiled for all 16 species so far known from Borneo and Sumatra. The high morphological plasticity of the epigean species of Menimus should be re-examined in a more comprehensive study of all Gnathidiini, not only with morphological but also with molecular data.