[[Genus Rivulus ^ZBK ]]

The Neotropical killifish genus Rivulus Poey ^ZBK is a speciose assemblage with about 100 valid species occurring in most river basins of Middle and South America (Costa, 2003a, 2004a). The greatest diversity of the genus is concentrated in the area comprising river basins draining the Guiana Shield in northern South America, from where numerous species have been described in recent years (e.g., Costa, 2003b, 2004b, c; Huber, 1991, 1992; Lasso et al, 1992; Thomerson et al., 1991a, 1991b, 1992; Vermeulen & Isbrücker, 2000). Among them, two species of Rivulus ^ZBK endemic to the Rio Negro basin, Brazilian Amazon, R. romeri Costa ^ZBK and R. kirovskyi Costa ^ZBK, are unique among congeners in having a unique arrangement of supraorbital neuromasts and being the smallest species, reaching about 23 mm SL as adult maximum size (Costa, 2003b, 2004c). A third species of this group, collected in the Rio Uatumã basin, is herein described.