Plistonax difficilis

Plistonax difficilis (Melzer, 1934) (Fig. 48) Idiomerus difficilis Melzer, 1934b: 98. Melzerus difficilis; Monné, 2005b: 179 (cat.; comb. nov.). Plistonax difficilis; Silva Júnior et al., 2021: 510 (comb. nov.). Remarks. This species was described based on specimens from Brazil (São Paulo, Goiás, and Minas Gerais) and Argentina (Tucumán). Currently, it is known from Peru, Bolivia (Beni and Santa Cruz), Brazil (Rondônia, Mato Grosso, Goiás, Minas Gerais, São Paulo, Paraná, and Rio Grande do Sul), Paraguay, and Argentina (Tucumán and Formosa) (Bezark 2024, Monné 2024b, Tavakilian & Chevillotte 2023). Monné (2005b) provided a new name for Idiomerus Melzer, 1934 due to homonymy with Idiomerus Imms, 1912. According to Silva Júnior et al. (2021) on P. difficilis: “Femora with one yellow stain on inner surface of globose region (only males).” However, it was not informed, and was not used in the analysis that the males have a deep depression on the ventral surface of all femoral clubs with dense setae, and not a yellow stain as reported. This feature is absent in all other species of Plistonax Thomson, 1864. We believe that the synonym of Melzerus with Plistonax was a mistake. However, we prefer not to reinstate the genus here. Material examined. BRAZIL, Mato Grosso do Sul (new state record): Campo Grande, CNPGC [Centro Nacional de Pesquisas de Gado de Corte—EMBRAPA], 1 specimen (MNRJ-ENT-47627), 28.X.1976, W.W. Koller leg. (MNRJ).