Plochionocerus newtonorum Asiain, Márquez & Morrone, sp. nov.

Type material (3 specimens). Holotype, male: “ FRENCH GUIANA: Decembre / Guyane Francaise, Nouveau Chantier Collection Le Mount / fulgens F. det. Bernh. / Chicago NHMus M. Bernahuer Collection / Holotype Plochionocerus newtonorum Asiain, Márquez & Morrone, 2007 ”. (FMNH). Paratypes: “ Guyane Francaise, Nouveau Chantier Collection Le Mount / Mars / fulgens F. det. Bernh. / idem fourth label / Paratype Plochionocerus newtonorum Asiain, Márquez & Morrone, 2007 ” (FMNH, Ψ). “Fevrier / Guyane Francaise St-Laurent du Maroni Collection Le Mount / fulgens F. det. Bernh. / idem fourth label / Paratype Plochionocerus newtonorum Asiain, Márquez & Morrone, 2007 ” (FMNH, Ψ).

Description. Total length 19.7–21.2 mm. Metallic green or violet-blue.

Head. Almost rounded, 1.29–1.33 times as long as wide, almost as wide as pronotum (1.03–1.07 times), dorsally and ventrally flat (similar to Fig. 13); ventral surface with slightly dense, expanded, umbilicate punctures (10–19 in each half of head), arranged in “v” (similar to Fig. 50); first antennomere 1.64 times as long as antennomeres 2+3 combined, second antennomere 0.60 times as long as third antennomere, antennomeres 4– 10 moderately transverse, increasing in size toward antennomere 10, antennomere 9 as long as antennomere 10, apical antennomere in males 1.33 times as long as wide and as long as antennomeres 9+10 combined; mandibles with basal external channel (Fig. 63).

Thorax. Pronotum moderately oblong (length/width: 1.34–1.41); shorter than elytra (0.76–0.77 times their length); with two clearly visible, depressed areas in posterior third (Fig. 56). Prosternum moderately transverse (length/width: 0.72–0.80).

Aedeagus. Pear-shaped, length 3.86 mm, with parameres moderately long (0.35 times as long as median lobe); apical area of median lobe 0.27 times as long as the total length of median lobe, and internal sac conspicuously visible (Fig. 87).

Variation. One specimen has the mandibular channel slightly visible.

Comparative notes. Because of its rounded head, with its flat or almost flat dorsal surface, P. n e w - tonorum can be confused with P. hermani and P. transversalis . The species is differentiated from P. hermani in the Comparative notes of that species. Plochionocerus newtonorum can be distinguished from P. transversalis because antennomeres 4–10 are less transverse, the mandibular channel is present and the aedeagus has long parameres, and the internal sac is conspicuously visible.

Geographical distribution. French Guiana.

Etymology. We take pleasure in dedicating this species to Alfred F. Newton Jr. and Margaret K. Thayer (Field Museum of Natural History), for their constant support of our studies of Staphylinidae and their important contributions to the study of this group.