The new species appears to be closely related to B. kurilensis Zaitzev, but differs from it clearly in the outline of the male genitalia, particularly in the shape of the gonostylus.
Male. Head black. Mouthparts brown; palpi yellow. Clypeus dark brown. Antenna brown; first and base of second flagellomere yellow. Sixth flagellomere about 3 times as long as wide.
Thorax. Mesonotum dark brown to black, finely grey dusted with three more or less shining longitudinal stripes. Pleurae brown. Laterotergite bare.
Wing hyaline; veins yellow, except C and R brownish. C extending beyond tip of R5 up to middle of distance between R5 and M1. Sc bare, ending in C opposite to base of Rs. Sc2 located behind middle of Sc. R5 slightly bent. Stem of M fork 1.55–1.74 (1.58) times as long as ta. Base of Cu fork under base of ta. Haltere yellow.
Legs yellow; trochanters brown; hind coxa sometimes darkened at base. Fore tibia with 1 v and 1 pv. Mid tibia with 3 ad, 3–4 pd, 2–3 p, 2–3 av and 3–6 pv. Hind tibia with 6–8 ad, 9–10 pd, 2–4 av and 5–10 p. Ratios of tibia to first tarsomere for fore, mid and hind legs as: 1.34–1.40 (1.37); 1.50–1.62 (1.56); 1.80–1.97 (1.90). Fore tibia with one spur, mid and hind tibia each with two spurs (av spur about 0.75 times as long as pv spur).
Abdomen dark brown. Terminalia dark brown. Gonostylus in lateral view somewhat conical, with rather long basal process bearing two apical spines. Cerci with one apical comb of blunt-tipped spines and two basal rows of spinules. Gonocoxites sternally fused, with cleft dividing only apical parts of sternal submedian processes. Parameres short, not protruding outside apical margin of gonocoxites.
Female unknown.
Wing length 3.33–3.50 (3.43) mm.