Figs 12–14, 15F, 16
Type materials. Holotype. China: Male, Hainan, Baisha, Yinggeling National Natural Reserve, 21st August 2019, He Zhixin and Zhang Tao coll. Paratypes. 7 males, Hainan, Baisha, Yinggeling National Natural Reserve, 21st August 2019, He Zhixin and Zhang Tao coll.; female, Hainan, Baisha, Yinggeling National Natural Reserve, 21st August 2019, He Zhixin and Zhang Tao coll. (SNNU).
Description. Male. Body shape typical of the genus (Fig. 12A). Head small with a distinct red transverse groove which middle raised and sides sunken in front of pronotum. Rostrum slightly wider than antennal scape, faintly furrowed in the middle; vertex flatten. The apical segment of maxillary palpus distinctly widened; fourth and fifth segments of equal length, and a little shorter than the third one (Fig. 13A). Pronotum length nearly three times as head, and longer than width. Pronotal anterior margin straight, posterior margin convex, covering a portion of tegmen and reaching the base of mirror. Fore tibia internal tympanum large and oval, without external tympanum. Tegmen 1.1 times wider than the posterior area of pronotum; apical field convex; mirror roughly triangular, almost as long as width (Fig. 13B). Hind femur 1.2 times longer than hind tibia; hind tibia 2.2 times longer than hind metatarsus. Male genitalia visible externally. Abdomen: Supra-anal plate with last abdominal tergite and epiproct distinctly separated by a transverse suture (Fig. 14B). Last abdominal tergite transverse, distinctly narrowing posteriorly, rhombic; with dense setae both side of along the apical surface; anterolateral area with a compressed projection (Fig. 14B). Epiproct rounded, slightly less wide than posterior margin of last abdominal tergite; setose along posterior margin (Fig. 14B). Paraproct process medium-sized, slightly compressed in basal half; external side and apex black, internal side white; apical area styliform, acute (Figs 14A & C). Genitalia: Epiphallus membranous; external sclerites elongate, divided at basal and apical part, forming an angle; internal sclerites slightly curved (Fig. 15F).
Female. Apterous. Pronotum short, little longer than wide, scarcely narrowing in front. Abdomen ornamented with eight lines dorsally (Fig. 12B). Legs and cercus distinctly pubescent. Abdomen: Supra-anal plate armed with margins strongly and laterally narrowing; epiproct with apex rounded and setose. Ovipositor straight, apex with sparse hairs (Fig. 13C).
Colouration. Head reddish-brown; antenna with scapus and pedicellus brown, flagellum light brown; maxillary palps yellowish-brown. Pronotal disc clay bank, with white scales along the apical margin. Tegmen yellowish; in dorsal view, apex with broad black margin; black band not continuing to the lateral field. Femur pale orange. Abdomen with tergite orange, covered by yellow scales, but abdominal apex black. Male paraproct process black. Cerci light orange. Ovipositor yellowish-brown, the base and apical valves reddish-brown.
Calling Song. Echeme sequence period 6–14 s, echeme sequence duration continue 2–6 s with 4–8 s echeme sequence interval. Each echeme sequence includes 3–12 echemes. Each echeme period 0.5– 0.65 s, echeme duration 0.2– 0.25 s with 0.3 s echeme interval. Each echeme includes 3 syllables. Echeme sequence rate is about 6 syllables/ s. The dominant harmonic peak observed in the spectrogram is 6.2–6.5 kHz (Fig. 16).
Etymology. The name refers to its occiput with a distinctly red transverse groove, like the connection between head and pronotum is broken (Fig. 12A).
Measurements. Male (n=7): BL 9.10±0.8, PL 3.17±0.16, PW 2.45±0.13, TL 2.27±0.19, TW 2.83±0.14, HFL 4.45±0.28, HTL 3.64±0.58, HML 1.66±0.12; Female (n=1): BL 9.31, PL 2.13, HFL 4.68, HTL 4.13, HML 1.45, OL 5.66.
Remarks. This species is very similar to O. dowwiangkanae, O. peniculatus, O. tuberculatus and O. aureus. Their tegmina are yellow with dark brown band along posterior margin, but differs in the presence of external sclerite of male genitalia (Fig. 15). This species differs from all species above in the supra-anal plate being setose but without strong short hairs standing together as in a brush (Fig. 12B); and it is also similar to O. citrus, but different in colour of head and cerci. It is also different with O. panda in colouration of body and male genitalia.