The genus Callicebus is one of the most diverse Neotropical primate groups, with 31 recognized species. However, large knowledge gaps still exist regarding the diversity of this genus. Such gaps are gradually being filled due to recent intensification of sampling efforts. Several geographic distributions have been better delimited, and six new species have been described in the last 15 years. The goal of the present study is to describe a new species of Callicebus belonging to the Callicebus

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... och species group, recently discovered in an area previously considered to be part of the geographic distribution of C. cinerascens. Data collection was conducted through direct observations, specimen collection and interviews with local residents during four expeditions. Specimens were deposited in the mammalian collection of the Museu Paraense Emílio Goeldi. For a comparative evaluation, we examined specimens of the other species of the Callicebus moloch species group, especially the geographically neighboring forms, C. bernhardi and C. cinerascens. We examined 10 chromatic characters of the fur. In addition to body mass, we verified the conventional external variables and 26 craniometric variables. The new species differs from all other Amazonian Callicebus by an exclusive combination of characters, being easily distinguished by the light gray line of the forehead, dark ocher sideburns and throat, dark gray portions of the torso and flanks, and uniformly orange tail. The geographic distribution of the new species is limited by the Roosevelt and Aripuanã rivers, in the states of Mato Grosso and Amazonas, Brazil. Approximately 25% (1,246.382 ha) of this area falls within conservation areas, with five areas of sustainable use (746,818 ha) and three of integral protection (499,564 ha). Furthermore, a considerable portion of the distribution area is located within indigenous lands (1,555.116 ha -32%). Therefore, 57% (2,801.498 ha) of the occurrence area of the new species falls within protected areas.