(Presbytis siamensis)
The white-thighed surili (Presbytis siamensis) 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 (nominate),cana,paenulata and rhionis,are recognized here,but the taxonomy is disputed and in need of a review.