White-thighed surili (Presbytis siamensis)

The white-thighed surili is a species of primate in the family Cercopithecidae. It is endemic to the Thai-Malay Peninsula, the Riau Archipelago and Sumatra. Four subspecies, ''siamensis'' , ''cana'', ''paenulata'' and ''rhionis'', are recognized here, but the taxonomy is disputed and in need of a review, and it has included ''P. natunae'' as a subspecies, or alternatively both have been considered subspecies of ''P. femoralis''.