Agaporomorphusjulianeae sp. n. is described from the Biological Field Station Panguana, in Huànuco province of central Peru. The new species belongs to the Agaporomorphusknischi-group sensu Miller 2005. Together with Agaporomorphusknischi Zimmermann, 1921 and Agaporomorphuscolberti Miller & Wheeler, 2008 this is the third species of the genus with broadly enlarged male antennomeres. The new species can be separated from Agaporomorphuscolberti and Agaporomorphusknischi by the smaller please expanded male antennomere VIII, and the form of the median lobe. Important species characters (median lobe, male antennae, metafemur, colour pattern) of the new species and Agaporomorphusknischi are figured, and the habitat, a temporary blackwater forest pond, and its species rich water beetle coenosis are illustrated and described in detail. The Brazilian Agaporomorphusmecolobus Miller, 2001, only known from the type material from Sao Paulo, is here recorded for Minas Gerais. Habitus photos of four additional Agaporomorphus species and Hydrodytesopalinus (Zimmermann, 1921) are provided. Altogether ten species of Agaporomorphus are now known.