Inpaichthys kerri n. g. n. sp., um novo peixe caracídeo do alto rio Aripuanã, Mato Grosso, BrasilA new little Tetra (Pisces. Cypriniformes, Characoidei) belonging to a new genus Inpaichthys kerri n. g. n. sp., is described. It was collected near the field station of Instituto Nacional de Pesquisas da Amazônia (INPA), Núcleo Aripuanã, in the north of Mato Grosso - Brazil. This species has the lateral line incomplete and the caudal fin naked. The teeth are tricuspidate in two very irregular rows on the premaxilla. The inner row is usually composed of only 2 median teeth on each side. The maxilla is toothed on half of its edge, with usually 7 or 8 tricuspidate to conical teeth. This dentition in combination with other morphological characters described in the paper differentiate Inpaichthys from the other genera, of the subfamily Tetragonopterinae.