This species of monkey, Trachypithecus auratus (aka Javan lutung), was first described in 1812 by M. Etienne Geoffroy St. Hilaire, an early 19th Century French naturalist who named twenty-four primate species. Langurs are the Asian members of the Colobin sub-family of leaf-monkeys. As such they have the multi-chambered stomach of the African Colobus monkeys and spend much of their day in “langurous” digestive rest.
The animals at the Bronx Zoo are from an Eastern Java population who are orange-brown, rather than the more common brownish-black. Their tails are notably long, almost twice the length of the body. These pictures include one distinctly older animal, and another noticeably younger individual.