Arcotheres guinotae n. sp., is described from a single female collected from an unspecified locality in Thailand. This species, as well as A. similis (Bürger, 1885), A. spinidactylus (Gordon, 1936) n. comb., A. tivelae (Gordon, 1936) n. comb., and A. alcocki (Rathbun, 1910) n. comb., constitute a subgroup within this genus which is distinguished by the dactylus of the third maxilliped not reaching the tip of its propodus and the dactylus of the fourth walking leg being longer than that of the third walking leg. Arcotheres guinotae n. sp. differs from all the above species in the acute and sinuous anterolateral margin, the fourth walking dactylus is longer than that of the third and setae on the ventral margin of the fourth walking dactylus are longer than those of its dorsal margin.
Crustacea, Decapoda, Brachyura, Arcotheres guinotae n. sp., Thailand, new species.