Abstract: The pinnotherid genus Orthotheres Sakai, 1969, is re-diagnosed on the basis of the type species, O.
turboe Sakai, 1969, and two allied species, O. haliotidis Geiger & Martin, 1999, and a new species, O. baoyu, from
the South China Sea. The genus is characterised by its transversely ovate female carapace with the front visible
from dorsal view, a long third maxilliped ischiomerus which is completely fused, the third maxilliped propodus
is elongate and extends beyond the articulation with the dactylus, which is inserted subterminally on it, short
ambulatory legs, which have a distinctly hooked dactylus, and the dactylus of the second and third legs in which
the ventral surface is prominently excavated. The generic affinities of the other species now referred to Orthotheres
are also discussed at length. The new species is described, figured and compare with congeners.