Two new species of land-dwelling crabs of the genus Geosesarma De Man, 1892 (Crustacea: Brachyura: Thoracotremata: Sesarmidae) from Bintan Island, Indonesia

Specimens of land-dwelling sesarmid crabs from two localities in Bintan Island (Riau Archipelago, Indonesia) belong to two new species of the genus Geosesarma De Man, 1892, and are here described. One higher altitude species (G. raj, new species) is characterised by bright colours in life, elongated ambulatory legs and the absence of an exopodal flagellum on the third maxillipeds. A lowland species (G. bintan, new species) is characterised by duller coloration, proportionately shorter legs, and the presence of an exopodal flagellum on the third maxillipeds. The gonopod structures of both species are also diagnostic. The two new species are compared with their closest congeners from Singapore and Peninsular Malaysia. With these two descriptions, 51 species are now known in Geosesarma.