Balala mekongia Tang & Zhang sp. nov.

(Figs. 9, 11)

Length (including forewing): ♂ 11.29–11.51 mm.

External morphology. Body brownish-red to dark brown. Crown (Fig. 9G) anterior margin round, length shorter than 1/2 width between eyes. Exposed part of mesonotum and scutellum (Figs. 9F, I) approaching or even reaching apex of clavus, exposed part of mesonotum about 1/8–1/6 scutellum length, scutellum moderately swollen and slowly declining toward apex, median longitudinal ridge very strong and extended entire length of scutellum. Forewing with one transparent band present between apical cells and appendix. Abdomen with pair of continuous yellow patches mainly on 5th and 6th tergites submedially. Hind femur with 4 macrosetae, tibia with ca. 11–12 setae in rows AD, PD, respectively.

Male genitalia. Pygofer (Figs. 11 A–F) with dorsal inner margin wavy, subapex of ventral margin with pair of small teeth, few small short setae arranged along ventral margin; ventral appendage tapering and extended slightly beyond teeth, apex slightly curved dorsad, with one small subapical tooth. Subgenital plate shorter than pygofer side. Apical margin of connective emarginate; style about 1.7x longer than connective; aedeagus shaft tubular with pair of slender processes at apex, preatrium broad and slightly shorter than shaft, gonopore between processes at shaft apex.

Material examined. Holotype ♂: Vieng Vai, Thailand, 23–24. IV.1920, R. V. de Salvaza (BMNH) . Paratype 1♂: Haut Mekong, Vieng Vai, Thailand, 3–8.VI.1918, R. V. de Salvaza (BMNH) .

Etymology. This species is named for its type locality, the river Mekong.

Remarks. This species is extremely similar to Balala karenia both in morphology and genitalia but the latter has a pair of small horn-like processes on basal part of the aedeagal shaft submedially.