Genus Chalybion Dahlbom, 1843

Chalybion Dahlbom, 1843:21

Type species: “ Chalybion caeruleum ” [= Sphex caeruleus of Linnaeus, 1767: 941 = Sphex caeruleus Linnaeus, 1763 (nec Sphex caeruleus Linnaeus, 1758) = Sphex cyaneus Fabricius, 1775 (nec Sphex cyaneus Linnaeus, 1758) = Pelopeus (sic) californicus de Saussure, 1867], designated by Patton, 1880: 378.

Chalybion Agassiz, 1846: 77 . Emendation of Chalybion Dahlbom, 1843, junior homonym of Chalybion Agassiz, 1846 .

Hemichalybion Kohl, 1918: 79 . Type species: Pelopoeus eckloni Dahlbom, 1845, designated by Pate, 1937: 30.

Key to species from northwestern Vietnam

Females

1. Lower metapleuron with conspicuous carina above midcoxa; area between antennal sockets with transverse carina....... 2

- Lower metapleuron without conspicuous carina above midcoxa; area between antennal sockets flat.................... 3

2. Mesosoma elongate, about 4 times as long as high; petiole shorter than hind basitarsus; forewing light brown with apical margin infuscate.................................................................. C. dolichothorax (Kohl) (Fig. 12)

- Mesosoma less than three times as long as high; petiole longer than hind basitarsus; forewing hyaline C. gracile Hensen (Fig. 13)

3. Sixth metasomal sternum flat and wide, broadly truncate at apex................................................ 4

- Sixth metasomal sternum not markedly wide, rounded at apex.................................................. 5

4. Distal area of both forewing and hindwing brown, proximal area hyaline; petiole moderately curved................................................................................................ C. malignum (Kohl) (Fig. 15)

- Both forewing and hindwing light brown; petiole markedly curved.................. C. tanvinhensis sp. nov. (Figs. 1‒6)

5. Anterolateral area of propodeum without tomentum; petiole markedly curved........... C. japonicum (Gribodo) (Fig. 14)

- Anterolateral area of propodeum with tomentum; petiole moderately curved........... C. bengalense (Dahlbom) (Fig. 11)

Males. Males of C. dolichothorax and C. gracile are unknown and not included

1. Anterior margin of clypeus without tooth; eighth and ninth flagellomeres with placoids; petiole markedly curved................................................................................ C. tanvinhensis sp. nov. (Figs. 7‒10)

- Anterior margin of clypeus with five teeth; placoid varied; petiole moderately to markedly curved..................... 2

2. Anterior margin of clypeus with five rather small teeth; seventh to ninth flagellomeres with placoids; petiole moderately curved.............................................................................. C. malignum (Kohl)

- Anterior margin of clypeus with five broader teeth; placoid varying............................................. 3

3. Eighth and ninth flagellomeres with placoids; anterolateral area of propodeum without tomentum.. C. japonicum (Gribodo)

- Fifth or sixth to ninth flagellomeres with placoids; anterolateral area of propodeum with tomentum.................................................................................................... C. bengalense (Dahlbom)