The endophallic structure of the genus Laius is studied and discussed based on the examination of 19 species from Asia to the Indian Ocean. The structure contains two primary sclerites (named gonoporal piece and ligula), a secondary sclerite on the basal part of the gonoporal piece (named additional sclerite) in some species, and a membranous basal area closely covered with many spines (named spinous area). Five species groups are recognized based on the morphology of the endophallic sclerites. The sympatric species have different body sizes and quite distinguishable endophallic sclerites (= different species group), while the allopatric species have overlapping body sizes and similar endophallic sclerites (= same species group). Three new species are described and six previously known species are redescribed with endophallic sclerites, and the descriptions of endophallic sclerites of the remaining ten species are added. The larva of Laius rodriguesensis sp. nov. is also described. The genus Nossibeus Evers, 1994 is synonymised with Laius Guérin-Méneville, 1830.
Melyridae, taxonomy, distribution, endophallus, new species.