Clarifying the identities of the Asian potamid genera Potamiscus Alcock, 1909, Ranguna Bott, 1966, and Dromothelphusa Naiyanetr, 1992 (Crustacea: Brachyura: Potamoidea).

The confused and intertwined identities and taxonomic histories of three Asian freshwater crab genera, Potamiscus Alcock, 1909, Ranguna Bott, 1966, and Dromothelphusa Naiyanetr, 1992, are reviewed and clarified. Ranguna, long assumed to be a junior synonym of Potamiscus (itself, until 2003, considered a junior synonym of Potamon Savigny, 1816), is recognised here as a valid genus, with the sole representative, Ranguna rangoonensis (Rathbun, 1904), shown to differ from Potamiscus species by carapace, third maxilliped, male thoracic sternal, male pleon and gonopod structures. Potamon (Potamiscus) decourcyi Kemp, 1913, is also transferred to Ranguna. The only known species of Dromothelphusa (originally established to replace Ranguna), D. longipes (A. Milne-Edwards, 1869), is known mostly from very old and dried museum material and treated here in detail based on fresh-collected adult male specimens. The three genera are rediagnosed and illustrated in detail. [ABSTRACT FROM AUTHOR]