Chalybion tanvinhensis Pham & Ohl & Truong 2019, sp. nov.

Chalybion tanvinhensis Pham & Ohl, sp. nov. (Figs. 1‒10)

Material examined: Holotype, ♀, pinned (deposited in IEBR, VAST), VIETNAM: Hoa Binh, Tan Vinh, Luong Son, 2.v.2017, Phong Huy Pham [IEBR]. Paratypes (IEBR, VAST): VIETNAM: Son La: 2 ♂♂, Chieu Village, Muong Thai, Ham Yen, 11.viii.2017, Phong Huy Pham [IEBR].

Diagnosis: Chalybion tanvinhensis is a member of the C. fabricator species-group because of the following combination of characters: Anterior margin of clypeus with five distinct teeth (median three close together, lateral teeth sharp and rather distant from others), integument dark blue, tarsi without plantulae, lower metapleuron area without angular carina, a rim at propodeal base only behind metanotum, metapleuron distinctly depressed below level of mesopleuron and side of propodeum, sixth metasomal sternum of female flat and apically broadly truncate.

This species can be easily distinguished from the other seven species of the C. fabricator species-group known so far by the following combination of characters: forewing homogenously, light brownish; fourth metasomal sternum of female without micropubescence; median and submedian teeth of clypeus well separate; vertex finely, sparsely punctate; mesoscutum weakly transversely strigose, interspaces shallowly punctate; petiole markedly curved, much shorter than the hindbasitarsus; antenna black; mesopleuron coarsely, densely punctate; metasoma with violaceous reflections. Because males of the fabricator species-group are known only for C. hainanense, C. malignum and C. sulawesii, the male of this new species can easily be separated from them by having the clypeus without teeth and no placoids on seventh to ninth flagellomeres.

This new species is similar to C. lividum and C. sulawesii, but it can be distinguished from the first by having black antenna, the median tooth of the clypeus much narrower than submedian teeth, the metasoma with violaceous reflections; from the latter by having lateral teeth of the clypeus in the female rather sharp; the forewing slightly, rather unevenly brownish; the medial and submedial cells most uniformly hyaline; petiole markedly curved, much shorter than the hindbasitarsus.

The male of C. tanvinhensis is unique in Chalybion in having the following characters: clypeus without lateral tooth, median and submedian tooth fused into single protruding lobe, placoids on seventh to ninth flagellomere (similar to C. japonicum (Gribodo, 1882), C. ohli Dollfuss, 2016 and C. zimmermanni Dahlbom, 1843).