The dubious titi monkey, Callicebus dubius

Hershkovitz named in 1988 for the first time a new species of titi monkey for the area between the Río Purus and Río Madeira. As the species didn’t fit very well in his theories about Callicebus evolution and dispersion, he named the species Callicebus dubius. In 1990 he gives a full description; the species has a buffy or whitish frontal tuft or transverse blaze present, crown anterior to ears blackish; sideburns, most of outer surface of forearms, and legs reddish; cheiridia blackish or reddish brown; skull essentially as in the moloch group, but with line between frontal bones about as long as straight line between parietals, palate across molars extremely wide.

It is thought to differ from Callicebus cupreus discolor (sensu Hershkovitz) by a pronounced blackish coronal band bordering whitish frontal blaze and dominantly blackish or reddish brown cheiridia.
Groves (2001) considers this species as a junior synonym of Callicebus cupreus, but other authors accept Callicebus dubius as a valid species and provide additional information on its distribution in Brazil (Roosmalen et al. , 2002 and Röhe and Silva Jr., 2003). Roosmalen et al. (2002) included Boliva in the distribution range of Callicebus dubius;  however, Mercado and Wallace (2010) report that the reddish titi monkeys living in northern Bolivia probably belong to another species.