1. Anterolateral border with about ten short, irregular teeth with obtuse apices. The surface of the carapace and chelipeds is irregularly hollowed giving it a reticulated appearance; P5 dactylus with spiny granules, larger in terminal; G1 see Serène, 1984, fig.101..................................................................................... M. nudipes

–Anterolateral border with 4–five teeth or lobes......................................................................................................2

2. Anterolateral border with five teeth, front sinuous, with produced and wide outer lobes, make a 4-teeth look............................... ................................................................................................................................................3

–Anterolateral border with four teeth, front with not produced and narrower outer lobes...................................4

3. Carapace regions with areolae sharper, separated by large deep grooves; chelipeds palm armed with prominent tubercles on superoexternal margin; G1 with 5–16 sawtooth-like extensions on ventral brim.............................................................................................................................. M. quinquedentatus

–Carapace regions slightly projecting, separated by broad, shallow furrows; chelipeds only with rugose on superoexternal margin, external surface smoother; G1 with the ventral brim curling inward with very fine blunt extensions................................................................................................... M. crassimanus

4. Anterolateral border with 4 feeble lobes, first two are sometimes not easily distinguished one from the other; surface of carapace and chelipeds have small hollows, giving them a slightly rugose aspect; P5 dactylus with granules, larger in terminal; G1 see Buitendijk, 1960 fig. 9j....................................................... M. demani

–Anterolateral border with 4 distinct teeth; surface of carapace and chelipeds with granules..........................5

5. Carapace regions noticeably projecting, separated by deeper and more acute furrows; anterolateral teeth with noticeably projecting apices forming an acute angle; surface of carapace and chelipeds is irregularly granular. the granules are much larger and more acute on the frontal margin, tantero-lateral teeth and neighboring regions, superoexternal parts of the carpus and propodus of the chelipeds and the anterior margins of the ambulatory legs; rows of transverse, irregular, acute granules occur here and there on the carapace regions. G1 see Serène, 1984, fig. 102............................................................................... M. voeltzkowi

–Carapace regions hardly projecting, separated by feeble furrows......................................................................6

6. Front produced, not double-rimmed; anterolateral teeth broader, apices slightly projecting, forming an obtuse angle; ambulatory legs carpus with three crests, dactylus without distinct subterminal tooth........................................................................................................................................... M. distinguendus

–Front not so produced, double-rimmed; anterolateral teeth narrower, apices projecting forming an acute angle; ambulatory legs carpus without obvious crests, a sharp and strong subterminal tooth on dactylus of last three legs...........................................................................................................................................................7

7. P5 slender, especially the obvious prolonged propodus and dactylus; dactylus tip prolonged, curved backward; the color of fixed finger extending to palm irregularly in male chelipeds; G1 more stout, distal tip with a apical lobe slightly upturned, the apical lobe dorsal rim more prominent than the ventral rim........................................................................................................................................................M. orientalis

–P5 stout, dactylus tip stout, nearly straight, slightly pointed forward; the colour of fixed finger nearly not extend to palm in chelipeds; G1 more slender, apical lobe not upturned, the ventral rim more prominent than the dorsal rim........................................................................................................... M. hainanensis sp. nov.