ABSTRACT Xenelmis is one of the 51 Neotropical genera of the aquatic beetle family Elmidae and is currently represented by 15 species distributed throughout the Neotropics. This genus of tiny beetles is especially well represented in South America, where all but one species can be found, and Brazil has the greatest richness, with ten species recorded so far. Here we describe and illustrate Xenelmis tuchaua sp. nov., a new Elmidae species with remarkable sexual dimorphism and unique diagnostic characteristics. The new species was found in an Amazonian stream located in Mount Roraima National Park, Roraima state, Brazil. We provide an updated species list for Xenelmis with comments on the occurrence of sexual dimorphism in the genus.

RESUMO Xenelmis é um dos 51 gêneros neotropicais da família de besouros aquáticos Elmidae. O gênero é atualmente representado por 15 espécies distribuídas pelo Neotrópico. Esse gênero de diminutos besouros é especialmente bem representado na América do Sul, onde apenas uma das espécies conhecidas não ocorre, e o Brasil possui a maior riqueza, com dez espécies registradas até o momento. Aqui nós descrevemos e ilustramos Xenelmis tuchaua sp. nov., uma nova espécie de Elmidae com marcado dimorfismo sexual e características diagnósticas únicas. A nova espécie foi encontrada em um riacho amazônico localizado no Parque Nacional do Monte Roraima, estado de Roraima, Brasil. Fornecemos uma lista atualizada das espécies conhecidas de Xenelmis, com comentários sobre a ocorrência de dimorfismo sexual no gênero.

A taxonomic key for the genera of Elmidae (Coleoptera, Byrrhoidea) occurring in Goiás State, Brazil, including new records and distributional notes. Despite their great diversity and high abundance in Neotropical aquatic environments, the fauna of Elmidae remains practically unknown in some areas and even entire biomes in this region. In this work we bring, for the first time, faunistic data for the Elmidae of central Brazil. The aim of this work was to inventory the Elmidae fauna in central, southwestern and southeastern Goiás State, Brazil and to produce a taxonomic key, at genus level, for adults from the studied region. The taxonomic key presented herein offers means for the identification of all the 13 genera known to occur in Goiás, 11 of them being new records for the State. Moreover, the number of named species registered for Goiás increased from one to nine.