The black-browed titi monkey, Callicebus castaneoventris

In 1866 Gray described a new titi monkey under the name Callithrix castaneoventris from a specimen originating from Brazil and presented in the collection of the British Museum of Natural History in London. He described the species as having “the fur dark blackish grey, minutely punctuated with grey; outside of limbs reddish-washed; forehead, hands, and feet black; whiskers, throat, chest, belly, and inside of the limbs dark-red chestnut; tail black, tip washed with white; hair of tail black the whole length, except near the end, where the tips of the hairs are white.
In his Catalogue of Monkeys, Lemurs and Fruit-eating Bats in the collection of the British Museum (Gray, 1870) he already questions the validity of the species, and wonders if it could be a synonym of C. caligata (Wagner, 1843).

It is now generally accepted that castaneoventris  is a junior synonym of Callicebus caligatus.