Abstract
A new freshwater crab is described from a montane area in northern Taiwan based on morphological characters and molecular evidence. Geothelphusa cilan sp. nov., from the Cilan Forest, situated on the boundary of Hsinchu and Yilan (= Ilan) counties, is close to G. monticola Shy, Ng & Yu, 1994, and G. takuan Shy, Ng & Yu, 1994, but can be distinguished by its male first gonopod (G1) and the ratio of thoracic sternites. Molecular evidence from mitochondrial cytochrome oxidase subunit I (COI) also supports the identity of the new species.