1. Abdomen simple in structure, without sensory setae, patch or excavation; metafemora strongly modified (fig. 28)............................................................................ (B. uenoi species group) B. femoralis sp. n.
- Abdominal tergites IV–VI with either specialized setae, or patch, or excavation; metafemora normal in structure.......... 2
2. Tergite IV with a large median excavation, tergites V–VI simple in structure............... (B. auritus species group)... 3
- Tergite IV lacking median excavation, tergites V–VI with either sensory setae, or patch or excavation.................. 7
3. Abdominal tergite IV with pair of lateral setiferous patches (figs. 10, 12, 14; Nomura, 2003: 168, fig. 2 -B; Löbl, 1974: 92, fig. 1)................................................................................................. 4
- Abdominal tergite IV lacking lateral setiferous patches (Nomura, 2003: 168, fig. 2 -D)............ B. subalpicolus (Nomura)
4. Excavation of tergite IV located near base, lateral setiferous patches large, tergite V modified (figs. 12–15).............. 5
- Excavation of tergite IV located near apex, lateral setiferous patches much smaller, tergite V unmodified (figs. 10–11; Nomura, 2003: 168, fig. 2 -B)................................................................................... 6
5. Tergite IV with lateral margins of excavation well-delimited by widely forked ridges, with pair of small setiferous patches mesal to ridges, median excavation of tergite V narrow (figs. 12–13)............................... B. chinensis sp. n.
- Tergite IV with lateral margins of excavations defined by indistinct parallel ridges, lacking setiferous patches mesal to ridges, median excavation of tergite V much wider (figs. 14–15).......................................... B. pulcher sp. n.
6. Length more than 2.00; tergite IV with base of excavation bearing filament structure (Nomura, 2003: 168, fig. 2 -B); aedeagus in lateral view with short ventral lobe, dorsal apophysis not split in apical half (Nomura, 2003: 170, fig. 4 -B).................................................................................................... B. satoi (Nomura)
- Length less than 1.75; tergite IV lacking filament structure (figs. 10–11; Löbl, 1974: 92, fig. 1); aedeagus in lateral view with distinctive elongate ventral lobe, dorsal apophysis bifurcate in apical half (fig. 16; Löbl, 1974: 93, fig. 3)... B. auritus (Löbl)
7. Abdominal tergite V with pair of lateral setiferous patches (Nomura, 1991: 384, fig. 116 -A–F; 387, fig. 117 -A–B)........................................................................................... B. fragilis species group
- Abdominal tergite V lacking lateral setiferous patches (Nomura, 1991: 387, fig. 117 -C; Kurbatov, 1990: 74, fig, 2 -A)..... 8
8 Abdominal tergite V with broad and sparse setae at posteromedian margin; tergite VI with very broad excavation on basomedian portion, apex lacking specialized long setae (Nomura, 1991: 387, fig. 117 -C)........... B. transformis species group
- Abdominal tergite V with much narrower and denser setae at posteromedian margin; tergite VI with excavation also narrow, apex with tuft of specialized long setae (Kurbatov, 1990: 74, fig, 2 -A)...................... B. admonitor species group