Periacma platygnatha Wang, sp. nov.

(Figs 10, 25, 40)

Type material. CHINA, Guangxi: Holotype ♂, Mt. Lianhua (24º15′N, 110º11′E), Mt. Dayao, Jinxiu, 1000 m, 22.VII.2015, leg. MJ Qi & SN Zhao, slide No. LiSR16014 . Paratypes: 1♂, same data as holotype; 1♀, Hekou, Mt. Dayao, Jinxiu, 823 m, 18.VII.2015, leg. MJ Qi & SN Zhao; 39 ♂ 2♀, Jinxiu, Mt. Dayao, Jinxiu County, 578 m, 24‒ 25.VII.2022, leg. H Sun et al., slide Nos. XZX20685♂, XZX20686♂, XZX20687♂, XZX20690♂, XZX20691♂, XZX20689 ♀; 3♂, Jinxiu, Mt. Dayao, Jinxiu County, 866 m, 20.VII.2022, leg. H Sun et al., slide Nos. XZX20692, XZX20693 .

Diagnosis. The new species can be distinguished from its congeners by the gnathos having a lunate ventral plate, the sacculus with distal 1/3 produced to a spine-shaped process bearing a ventral denticle, and the aedeagus with a cluster of fine spines near apex.

Description. Adult (Fig. 10). Wingspan 12.0 ‒ 14.0 mm.

Head. Vertex and frons yellow. Labial palpus yellow; male first segment black, second segment dark brown in distal half on outer side; female second segment black at apex, with dense black scales in distal half on outer side, third segment with a few black scales on ventral side. Antenna with scape yellow on ventral surface, black except terminally yellow on dorsal surface; flagellum yellow, ringed with black on dorsal surface.

Thorax. M esonotum yellow, longitudally with dense black scales in middle; tegula yellow, with a few black scales. Forewing orange yellow, with scattered black scales; black spot at base of costal margin; black speckle from base of dorsum obliquely outward to basal 1/5 of wing above fold, then extending downward and along fold to dorsum; discal spot black, oblique; postmedial fascia black, uniformly wide from costal 3/5 to tornus; apical fascia black, narrowed along termen, not reaching tornus; fringe yellow, mixed with a few black scales along termen. Hindwing and fringe grey. Legs yellow, except three distal tarsomeres of fore- and midlegs black; on dorsal surface, foreleg with dense black scales on femur, with sparse black scales on tibia, midleg black at base of tibia, tarsus black at middle of first tarsomere and at base of second tarsomere.

Male genitalia (Fig. 25). Uncus narrow and parallel from near base to beyond middle, thereafter dilated elliptically, narrowly rounded at apex, with a seta near base laterally. Gnathos with ventral plate broad lunate, finely spinous in anterior half. Valva with costal part narrower in basal 1/3, subparallel in distal 2/3, rounded at apex; costa concave before middle; dorso-proximal process very short, setose apically; sacculus about 1/3 length of costal part of valva, slightly narrowed from broad base to basal 2/3, distal 1/3 produced to a large spine-like process, pointed and curved apically, with a denticle near apex on ventral margin. Saccus sub-rectangular. Aedeagus 3/5 length of costal part of valva, slightly widened from base to middle, thereafter tapered to about basal 5/6, produced to a digitate process distally, with a cluster of thorns near apex.

Female genitalia (Fig. 40). Papilla anale rounded on posterior margin.Apophysis anterioris about half length of apophysis posterioris. Eighth sternal plate concave at middle, with long setae posteriorly, anterior edge sclerotized. Ductus bursae membranous, thick. Corpus bursae membranous, elliptical, with dense spinules; signum being a small elliptical plate with two denticles.

Distribution. China (Guangxi).

Etymology. The specific epithet is derived from the Greek platy- and gnathus, referring to the large gnathos.