Generic characters of Platydialepis Haupt, 1941 are presented. A new species of the genus, P. amamiensis sp. nov. from the Amami Islands, the Ryukyus, Japan, is described, and another species of the genus, P. ryoheii Ishikawa, 1957, distributed in Honshu, Shikoku and Kyushu, Japan, is redescribed. Their biological notes are also given. A new combination is proposed: Platydialepis taiwaniana (Tsuneki, 1989) (=Malloscelis taiwaniana Tsuneki).