Key to the three known species of Prochetostoma Han

1 Scutum dark brown; crossvein r-m situated distinctly proximal to mid length of cell dm; short brown marking extending from costal margin at middle of cell r1 separate from transverse marking covering crossvein r-m......... P. contemnens (Hering)

- Scutum entirely yellow brown; crossvein r-m situated slightly distal to mid length of cell dm; short brown marking extending from costal margin at middle of cell r1 connected to transverse marking through crossvein r-m(Fig. 3 b)................. 2

2 Transverse marking covering crossvein r-m connected or nearly connected to apical C-shaped band covering crossvein dm-cu at posterior margin of cell cua; apex of C-shaped band not expanded; Ƥ with 3 pairs of lateral dark markings on T3–5; 3 abdomen with markings only on T5............................................................. P. bhutanicum Han

- Transverse marking covering crossvein r-m clearly separate from apical C-shaped band covering crossvein dm-cu at posterior margin of cell cua; apex of C-shaped band expanded (Fig. 3 b); both sexes with 3 pairs of lateral dark markings on T3–5................................................................................. P. expandens Sueyoshi & Han