A new genus of freshwater crab, Rajathelphusa gen. nov., and two species, R. ala sp. nov. (type species) and R. muni sp. nov., are described from the Kerala part of the Western Ghats biodiversity hotspot, India. The new genus is superficially similar to Arcithelphusa and Cylindrotelphusa from the same hotspot, but can easily be distinguished by the following suite of carapace and gonopod characters: an inflated
carapace with distinct epigastric and postorbital cristae; the third maxilliped exopod has a long flagellum; male sternites 2 and 3 separated by a shallow median groove while sternites 3 and 4 are completely fused, demarcated by shallow oblique grooves; a male first gonopod that is almost straight with a short distal conical distal segment; and a male second gonopod that is as long as the first gonopod with a long and slender distal segment. The two new species can be differentiated from each other by the lateral margins of male pleonal somite 6 and the structure of the male first gonopod.
Taxonomy, New freshwater crab, Gecarcinucoidea, Kerala, Idukki, Arcithelphusa, Cylindrotelphusa.
