Thyanta (Argosoma) emarginata Rider, 1991

Thyanta (Argosoma) emarginata Rider , new species

Figs. 260-264, Map 3

Description. Dorsal surface olive-brown, head and anterior two-thirds ofpronotum slightly darker; apex of scutellum reddish; punctures reddish-brown.

Apex of head evenly rounded; outer jugal margins sinuous, nearly parallel for middle third of distance from eyes to apex ( Fig. 261); surface of head rather densely punctate, juga appearing somewhat reticulate. Antennae pale brown, some reddish hues on distal 3 segments. Anterolateral margins ofpronotum straight in dorsal view; humeral angles rounded, nearly angulate, apex piceous, protruding slightly beyond base of adjacent coria ( Fig. 260). Surface of pronotum transversely depressed just posterior to pronotal cicatrices; each pronotal cicatrice marked with fuscous in mesial angle. Hemelytra rather uniformly punctate; posterior margins weakly convex; costal angles reaching beyond middle of penultimate connexival segments ( Fig. 260); hemelytral membranes hyaline. Connexiva narrowly exposed, stramineous; posterolateral angles of segments piceous.

Ventral surface pale yellowish brown; punctures concolorous. Rostrum stramineous, segment four black on apical half, reaching to near posterior margin of third (second visible) abdominal stemite. Ostiolar canals acuminate apically. Femora and tibiae stramineous to pale brown. Postspiracular black spots absent; posterolateral angles of abdominal sternites piceous.

Mesia! margins of basal plates in caudoventral view slightly convex; posterior margins sinuous; posteromesial angles deeply excavated; concavity resulting from excavations in basal plates nearly as long as wide, with lateral sides nearly parallel ( Fig. 262); surface of basal plates distinctly rugose, area near excavation fuscous. Sclerotized rod relatively elongate, not at all swollen subapically; dilation of spermatheca single, but abruptly narrowed for distal two-thirds of length of sclerotized rod ( Fig. 263); spermathecal duct moderately swollen and coiled below proximal flange ( Fig. 264). Male unknown.

Measurements. Total length 8.36; total width 5.41; medial length of pronotum 1.73. Medial length of scutellum 3.50; basal width 3.20; width at distal end of frena 1.21. Length of head 1.70; width 2.12. Length of segments 1-5 of antennae 0.49, 0.83, 0.99, 1.18, and 1.25, respectively. Length of segments 2-4 of rostrum 1.32, 0.88, and 0.87, respectively.

Holotype. 't labeled " Peru. Dpto. La Libertad Cumpang. above Uctubamba . 2625 M. 13 X 1979. L. J. Barkley." Deposited in the U.S. National Museum of Natural History (Washington, D.C.). No paratypes .

Distribution. Peru ( Map 3).

Comments. Although several species of Thyanta are known to have the posteromesial angle of the basal plates weakly emarginate, only three have this angle deeply emarginate. The resulting concavity in the basal plates of T. vadosa is much more shallow and the sides are divergent; both T. emarginata and T. excavata have the concavity deeper, with the sides nearly parallel. Thyanta emarginata differs from T. excavata by having the resulting concavity nearly as long as wide, and by the distinctly rugose surfaces of the basal plates, which are weakly rugose in T. excavata.

Thyanta emarginata further differs from both T. vadosa and T. excavata by the structure of the spermatheca. The sclerotized rod in T. emarginata is not swollen subapically as it is in T. vadosa and T. excavata. The nonswollen sclerotized rod is a character that T. emarginata shares only with T. hamulata , T. brasiliensis , and T. boliviensis. None of these three species have the basal plates excavated.

Etymology. Named for the distinctly emarginate posteromesial angles of the basal plates.