Abstract
Rivulus uatuman, new species, from the Rio Uatumã drainage, central Amazonian basin, Brazil, is described. It is a member of an assemblage including R. amanapira, R. atratus, R. ornatus, R. kirovskyi, R. rectocaudatus, R. romeri, R. tecminae, and R. uakti, diagnosed by a unique pattern of frontal squamation and a derived color pattern of the infraorbital region. It shares three unique derived conditions with R. kirovskyi and R. romeri: small maximum adult size, third anterior supraorbital neuromast posteriorly positioned and absence of vomerine teeth. The new species differs from R. kirovskyi and R. romeri by having the dorsal fin posteriorly positioned, fewer pectoralfin rays, more vertebrae, and a white bar on the distal margin of the caudal fin in males.

Keywords: Fish, Cyprinodontiformes, Rivulidae, Rivulus, Neotropica, Amazon, systematics, taxonomy, new species

Introduction
The Neotropical killifish genus Rivulus Poey is a speciose assemblage with about 100 valid species occurring in most river basins of Middle and South America (Costa, 2003a,...

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