Stephen Nash’s titi monkey, Callicebus stephennashi

Roosmalen and colleagues described in 2002 a new species of titi monkey from specimens that were thought to be caught somewhere along the middle to upper Rio Purús. The species has the forehead and anterior portion of the crown black, sharply contrasting with the posterior portion of the crown, nape, dorsum and rump which are silvery or buffy mixed with brownish agouti or brownish-black. The lower arms and legs are bright red or sometimes dark red, like the sideburns, under parts, and inner sides of the limbs. The hands are entirely silvery or white, the proximal portion of the tail is silvery mixed with brownish agouti to blackish brown, then black mixed with white or buffy, and the distal half to two-third entirely white or buffy.

Later the distribution of the species was restricted by Röhe and Silva Jr. (2003) to the area between the left bank of the Rio Ipixuna and the right bank of the Rio Mucuim.