Genus Xenoctenus Mello-Leitão, 1938

Type species. Xenoctenus unguiculatus Mello-Leit „o, 1938, by monotypy (considered a nomen dubium by Carcavallo & Martínez 1967 but here validated).

Emended diagnosis. Xenoctenus species can be differentiated from other Xenoctenidae by the presence of flexible tarsi in both sexes (Fig. 10B). Males can be distinguished from other xenoctenids by the tip of the cymbium with a thick scopula, without macrosetae (Figs 5, 7A–C, 8, 11A–C, 12A–B, 13A, C). The palps also differ by the retrolateral tegular projection (RTP) being long, concave and located anteriorly (Figs 4A–C, 7A–C, 8, 11A–C, 12A– B, 13A, C). Females differ by a strongly sclerotized epigynum and the primary spermathecae long, with irregular margins, and secondary spermathecae anteriorly positioned (Figs 6, 9, 10A, 12C–D).

Species included. Xenoctenus gomezraggioi Carcavallo & Martínez, 1967, Xenoctenus kaatinga Faustino-Magalhaes & Santos sp. nov., Xenoctenus unguiculatus Mello-Leit „o, 1938, Xenoctenus vittatus (Mello-Leit„o, 1936) comb. nov., Xenoctenus pampeanus Mello-Leit „o, 1940; Xenoctenus patagonicus Mello-Leit „o, 1940 (nomen dubium); Xenoctenus proseni Carcavallo & Martínez, 1967 .

Distribution. The genus is known mostly from xeric environments in Argentina and northeastern Brazil (Caatinga domain), with isolated records in southern Brazil and northeastern Argentina (Figs 14–16). Records from Bolivia and Colombia (Carcavallo & Martínez 1967) require further confirmation.