In his catalogue of British Museum Crustacea, Adam White listed two swimming crabs from Borneo as a new species, Amphitrite argentata, but he did not provide a description and therefore the name was a nomen nudum. Later, Alphonse Milne-Edwards described the larger of these male specimens as Neptunus argentatus and credited the species to White. Now assigned to Monomia Gistel, 1848, M. argentata was recently considered to represent a species-complex; however, its nomenclature and taxonomy have been confused over a long period of time. Furthermore, the larger syntype examined by Alphonse Milne-Edwards is no longer extant. The present study compared the smaller extant M. argentata male of White, here designated as the lectotype, with the description by A. Milne-Edwards. This dried specimen was re-examined using X-ray and computed tomography scanning techniques in order to reveal the general morphology of the first male gonopod (G1). Fresh material was collected and identified with confidence as M. argentata. This species was redescribed to modern standards including illustrations, details of coloration and new scanning electron micrographs of the G1 were provided. The validity of this species was further endorsed by comparing DNA sequences with congeners from the South China Sea. To conclude, the type status, authority and associated species-complex of M. argentata are discussed.