This is the third Euthygomphus species found in Vietnam. The others are E. koxingai and E. yunnanensis (formerly thought to be E. parvus).
I refer to Oleg's paper "Reconsideration of the genera Merogomphus Martin, 1904, and Anisogomphus Selys, 1857, including erection of a new genus, with a new species and discussion of addition specimens from Cambodia" in Zootaxa 4171(1):51-76 for the details concerning the identification of these species.
|Male Euthygomphus schorri, near Bao Loc, Lam Dong Province, 12 June 2016|
|Same male at slightly different angle|