1. Pseudacteon quadrisetalis Liu et Cai

(Figs. 1A–F, 24A–B)

Pseudacteon quadrisetalis Liu et Cai, 2013: 54 .

Diagnosis. Female. Apical seta longer than maximum width of palpus; setal palisade 2/3 length of mid tibia; setulae below basal half of hind femur shorter than those of anteroventral row of outer half; tergite VI reduced to a narrow anterior strip in middle but each lateral quarter with 4 long and 4–5 short setulae; sternite VI clearly defined, with 4 very strong pin-shaped setae and some fine, long setulae; dorsum of oviscape with 3–4 short setulae on sub-apex of each side; venter of oviscape with 12–16 fine, long and transversely-inclined setulae arranged in two longitudinal rows.

Female. Frons (Fig. 1A) dark brown, with about 12–14 setulae. Frons with 2 pairs of supra-antennal setae, upper pair as high as lower fronto-orbital setae. Second row of frontal setae clearly concave, all four setae are equally distanced. Flagellomere 1 brown, subglobose. Palpus pale, very lightly tinged brown, with 4 long setae, apical one longer than maximum width of palpus.

Thorax brown. Scutellum with a pair of setae, posterior twice length of anterior. Legs yellowish brown. Ratios of lengths of fore tarsomeres 0.81: 0.77: 0.63: 0.61: 1, with all five bearing a setal palisade (Fig. 1C). Setal palisade extends 2/3 length along mid tibia and comprising 35–40 modified setulae (Fig. 1D). Setulae below basal half of hind femur shorter than those of anteroventral row of outer half (Fig. 1E). Wing (Fig. 1B) length 1.14–1.17 mm, width 0.57–0.59 mm, width/length 0.51. Costal index 0.38–0.39. Costal ratio 1.96: 1. Costal cilia 0.08 mm. Alula with 3 setae. Haltere brown.

Abdomen. Tergites brown with sparse minute setulae. Tergites II–V very much broader than long, but progressively narrowing from tergite II backwards. Tergite VI (Fig. 24A) reduced to a narrow anterior strip in middle but each side bears 4 long and 4–5 short setulae at rear margin. Venter brown. Sternite VI (Figs. 1F, 24B) clearly defined, with 4 very strong pin-shaped setae and some fine and long setulae. Oviscape brown. The dorsum of the oviscape arched, with 3–4 short setulae on sub-apex of each side. The venter of the oviscape with 12–16 fine, long and transversely-inclined setulae arranged in two longitudinal rows (Fig. 1F).

Male. Unknown.

Distribution. China (Liaoning, Jilin, Gansu).

Material examined. 2♀, Liaoning, Benxi, Mt. Wunv (41°19′58.76″N, 125°25′11.81″E), 5–Jul–2012, Meng Yang ; 1♀, Liaoning, Benxi, Erdaogou (41°7′50.66″N, 124°22′12″E), 4-Jul-2018, Jiao Zhang ; 2♀ (slides), Jilin, Yanbian, Wangqing, Mingyuegou (43°15′26.19″N, 129°55′35.23″E, 380 m), 7-Aug-2014; Jianfeng Wang ; 4♀, Jilin, Yanbian, Wangqing, Mingyuegou (43°15′26.19″N, 129°55′35.23″E, 380 m), 7-Aug-2014, Jianfeng Wang ; 1♀ (slide), Gansu, Wen County, Guanegou (33°55′12″N, 104°14′21″E; 2478 m), 10-Aug-2011, Yunlong Cai ; 1♀ (holotype), Gansu, Wen County, Guanegou (33°55′12″N, 104°14′21″E; 2478 m), 10-Aug-2011, Yunlong Cai ; 2♀ (paratyes), Gansu, Wen County, Qiujiaba (32°55′12″N, 104°19′12″E; 2270 m), 7-Aug-2011, Yunlong Cai .

Remarks. This species is easily recognized in having 4 very strong pin-shaped setae on abdominal sternite VI and transversely-inclined long setulae on the venter of the oviscape. In the key to European Pseudacteon (Disney & Withers 2009), the species runs to couplet 6, to P. fennicus Schmitz, 1927 . It differs from the latter in having 4 very strong, pin-shaped setae on sternite VI and 12–16 fine, long and transversely-inclined setulae on the venter of the oviscape. In the key to Pseudacteon of the Russian Far East (Disney & Michailovskaya 2000), the species runs to couplet 4, to the putative female of P. pullum Michailovskaya, but it is different in having a uniformly brown sternite VI, with pin-shaped setae and 35–40 modified setulae of mid tibia setal palisade.