Macrobrachium malayanum (Roux, 1934) stat. nov. (Decapoda, Palaemonidae) as a synonym of M. geron Holthuis, 1950, with notes on its distribution

Macrobrachium pilimanus malayanus (Roux, 1934) is synonymized with M. geron Holthuis, 1950 and accorded full species status as M. Malayanum (Roux, 1934) stat. nov. A lectotype is also designated. Variation within M. malayanum and differences between this species and M. pilimanus (De Man, 1879) are discussed, and the taxonomy of the species clarified. New records of M. malayanum are presented for Sarawak and Sumatra.