The species of the genus Arcastes Baly, 1865 from Oriental Region are revised. The type species is A. biplagiata Baly, 1865 by original designation. The genus Arcastes was erected by Baly based on a peculiar shape of the antennae. Subsequently, eight other species have been described in this genus. Up to now this genus was not revised, in particular the male and female genitalia have not yet been studied. Studies of the type material revealed, that A. biplagiata possess a very peculiar shape of median lobe and endophallic structures. Next to the genotype, only two valid species remain in this genus: Arcastes suturalis Jacoby, 1884 (with A. ismaili Mohamedsaid, 2000 as new synonym), and Arcastes dimidiata Laboissiere, 1929. Arcastes sumatrensis Jacoby, 1884 is a new junior synonym of Neolepta biplagiata Jacoby, 1884. All other species need to be transferred to other genera that will be subject of the ongoing revision of the Oriental Galerucinae. Distribution of the three species of Arcastes is restricted to Singapore, Malaysia, and Indonesia, southward to Java. In this paper we provide redescriptions of the genus and the valid species, including illustrations of external and genitalic characters, photographs of the primary type specimens, distribution maps and a key.
