Isoctenus guadalupei (Mello-Leitão, 1941) comb. nov. Figures 1−3 Ctenus guadalupei Mello-Leitão, 1941: 215, figs 23–24 (female holotype from Guadalupe Norte [-28.9408, -59.5624], Província de Santa Fé, Argentina, M. Birabén coll., deposited in MLP 15180, examined); World Spider Catalog 2019. Note. Type specimen with faded coloration and missing leg IV segments, except the femur and coxae. The male was matched by similarities of size and coloration, and by the close proximity from the type locality. Additional material examined. ARGENTINA. Corrientes: Mburucuyá, Parque Nacional Mburucuyá (Sendero Che Roga, -28.0049, -58.0365, 85 m. a.s.l., manual collecting), 1 male, 27–30.V.2011, G. Rubio, M. Izquierdo & L. Piacentinni coll. (MACN-Ar 30496). Diagnosis. Males of Isoctenus guadalupei comb. nov. (Fig. 2A) resemble those of I. ordinario (Polotow & Brescovit, 2009: fig. 9A–B) by the elongated dorsal branch of RTA, bifid tip of embolus and shape of median apophysis, but it can be distinguished by the presence of a basal retrolateral projection of embolus (RPE), shorter tibia of palp and cymbium, and embolus with larger base. Males of Isoctenus guadalupei also present a projection on each coxae IV (Fig. 1C), which is absent in I. ordinario. Females of Isoctenus guadalupei resemble those of I. ordinario by the cordiform shape of the median field of epigynum and anterior position of lateral fields projections, but can be distinguished by the median field less excavated apically (Fig. 2B) and the larger spermathecae and copulatory ducts (Fig. 2C). Description. Male (MACN-Ar 30496). Prossoma uniformly orange, darker in the dorsum; with brown thoracic groove and black rings around eyes; greyish dorsal opistossoma with light brown dorsal, folium-like marking (Fig. 1 A−B). Total length 10.20. Carapace 5.60 long and 4.35 wide. Eye diameters: AME 0.20, ALE 0.20, PME 0.25, PLE 0.24. Leg measurements: I: femur 6.90/ patella 2.80/ tibia 7.10/ metatarsus 6.87/ tarsus 3.00/ total 26.67; II: 5.93/ 2.55/ 5.80/ 5.90/ 2.55/ 22.73; III: 5.16/ 2.00/ 5.00/ 5.65/ 2.15/ 19.96; IV: 7.00/ 2.25/ 6.70/ 8.90/ 2.90/ 27.75. Leg spination: tibia I-II v2-2-2-2-2, r0, p0, III-IV v2-2-2, r1-1, p1-1; metatarsus I-II v2-2-2, r0, p0, III v2-2-2, r1-1-1, p-1-1-1, IV v1-1-1-1- 1-2, r1-1-1, p1-1-1. Coxa IV with a ventral projection (Fig. 1C). Palp (Figs 1D, 2A): tibia approximately two thirds of cymbium length; RTA with ventral branch subtriangular; tibia with short and curved ventral apophysis; cymbium with ventral retrolateral projection reduced and dorsal retrolateral projection rounded; short and laminar embolus, with bifid tip and short basal projection; robust median apophysis, with conical anterior and posterior projections. Female (MLP 15180). Coloration faded, ranging from light brown to beige in the whole specimen. Total length 11.60. Carapace 5.50 long and 4.20 wide. Clypeus 0.17 high. Eye diameters: AME 0.26, ALE 0.20, PME 0.31, PLE 0.27. Leg measurements: I: femur 5.20/ patella 2.50/ tibia 5.00/ metatarsus 4.20/ tarsus 1.80/ total 18.70; II: 4.70/ 2.60/ 4.40/ 3.80/ 1.60/ 17.10; III: 4.20/ 2.00/ 3.50/ 3.70/ 1.50/ 14.90; IV: 5.60/ -/ -/ -/ -/ -. Leg spination: tibia I-II v2-2-2-2-2, r0, p0, III-IV v2-2-2, r1-1, p1-1; metatarsus I-II v2-2-2, r0, p0, III v2-2-2, r1-1-1, p-1-1-1. Epigynum (Fig. 2 B−C): subrounded median field; lateral spurs short, partially covered by the median field and with a pointed tip. Spermathecae with rounded head and large base. Distribution. Corrientes and Santa Fé Provinces, northeastern Argentina (Fig. 3). Isoctenus ordinario is commonly found in the Parana Dominion of Brazil and Argentina, while I. guadalupei is only found in the Chacoan province (part of the Chacoan Dominion) (Fig. 3).

Published as part of Polotow, Daniele & Brescovit, Antonio D., 2019, Almost eight decades later: description of the male of Isoctenus guadalupei (Mello- Leitão, 1941) comb. nov. and redescription of the female, pp. 291-294 in Zootaxa 4683 (2) on pages 292-293, DOI: 10.11646/zootaxa.4683.2.8, http://zenodo.org/record/3772813