Fifteen species of Aguna Williams, 1927 (Hesperiidae: Pyrginae) are known from near Cacaulàndia in central Rondônia, Brazil; nine represent undescribed species. These nine, plus four additional new species discovered among material from other areas, are named and described: Aguna latifascia, Aguna coeloides, Aguna nicolayi, Aguna latimacula, Aguna penicillata, Aguna spicata, Aguna longicauda, Aguna panama, Aguna spatulala, Aguna similis, Aguna mesodenlala, Aguna squamalba, Aguna parva. The species of Aguna are placed into ten species groups based upon the characters of the male and female genitalia. These groups are described and their included species are discussed. Aguna williamsi Hayward, 1935, new synonymy is considered synonymous with Eudamus glaphyrus Mabille, 1888, revised status. Goniurus hypozonius Plötz, 1880, new status is considered a subspecies of Eudamus aurunce Hewitson, 1867. Neotypes are designated for Goniurus cholus Plötz, 1880, Papilio coelus Stoll, [1781], Goniurus gideon Plötz, 1880, and Goniurus hypozonius Plötz, 1880. Lectotypes are designated for Eudamus asander Hewitson, 1867, Eudamus panthius Herrich-Schäffer, 1869, Eudamus scheha Plötz, 1882, Eudamus mega-clesMabille, 1888, Eudamus leucogramma Mabille, 1888, Hesperia metophis Latreille, [1824], Eudamus aurunce Hewitson, 1867, and Eudamus glaphyrus Mabille, 1888. Preliminary identification keys are provided.
Lepidoptera; Hesperiidae; Aguna; Neotropical