Key to species of the Stenus tenuimargo group from China

1. Elytra without orange spot.............................................................................. 2

- Elytra with orange spot................................................................................. 3

2. Elytra much longer than broad (EL: EW>1.3), sternum 9 apicolaterally with long teeth. Aedeagus as Figs. 19 & 20 A. Sper- matheca as Figs. 19 & 20 H............................................................. S. semilineatus Puthz

- Elytra slightly longer than broad (EL: EW <1.1), sternum 9 apicolaterally with moderate long teeth. Aedeagus as Figs. 1 E & 2 A...................................................................... S . nabanhensis Lv et Zhou, sp. nov.

3. Abdomen with distinct paratergites........................................................................ 4

- Abdomen without distinct paratergites but with a line-like lateral margination...................................... 7

4. Elytra spot broader, extending to the declining sides of elytra. Aedeagus as Figs. 5 & 6 A.......... S . jaccoudi Rougemont

- Elytral spot less broad, not extending to the declining sides of elytra............................................. 5

5. Elytra much broader than head (EW: HW>1.2). Aedeagus as Figs.17 & 18 A.......................... S . perroti Puthz

- Elytra less broad (EW: HW <1.15)........................................................................ 6

6. Paratergites with only one row of punctures. Aedeagus as Figs. 11–14 A. Spermatheca as Figs. 11 & 12 H.................................................................................................. S . notaculipennis Puthz

- Paratergites with dense, side by side punctures. Aedeagus as illustrated in Rougemont (1983b: Fig. 19) ..................................................................................................... S. subthoracicus Puthz

7. Species from Taiwan, elytra relatively broad................................................................ 8

- Species from Continental China, elytra less broad........................................................... 11

8. Elytra longer (EW: EL<0.92 [0.88–0.94]), elytral spot distinctly extending into anterior half of elytra.................. 9

- Elytra shorter (EW: EL>0.92 [0.93–0.98])................................................................ 10

9. Abdominal punctuation coarse and dense. Aedeagus as Puthz (2011: Fig. 107). Spermatheca as Puthz (2011: Fig. 21). BL: 5.0– 6.0 mm (FB: 2.6–2.8 mm)................................................................ S. miwai Bernhauer

- Abdominal punctuation less coarse, sparser. Aedeagus as Puthz (2011: Fig. 108). Spermatheca as Puthz (2011: Fig. 20). BL: 5.0–6.0 mm (FB: 2.4–2.7 mm)............................................................ S. mithracifer Puthz

10. Elytral spot smaller, not extending to the posterior margin of elytra, abdominal punctuation less coarse. Aedeagus as Puthz (2011: Fig. 116). Spermatheca as Puthz (2011: Fig. 16). BL: 5.5–6.5 mm (FB: 2.4–2.7 mm)........ S. electrigemmeus Puthz

- Elytral spot larger, extending to the posterior margin of elytra, abdominal punctuation coarser. Aedeagus as Puthz (2011: Fig. 19). Spermatheca unknown. BL: 6.5 mm (FB: 2.6 mm)..................................... S. electrigemmatus Puthz

11. Micropterous....................................................................... S. marginiventris Puthz

- Macropterous........................................................................................ 12

12. Abdominal punctuation coarser and extremely dense, interstices on tergite VII smaller than half diameter of punctures; smaller. Aedeagus as Figs. 21 &. 22 A............................................................. S . solstitialis Zheng

- Abdominal punctuation less coarse or sparser, interstices on tergite VII distinctly larger than half diameter of punctures... 13

13. Elytra trapeziform, elytral spot longer.................................................................... 14

Elytra subquadrate, elytral spot smaller................................................................... 15 14. Elytral spot about 2/3 as long as one elytron. Aedeagus as Puthz (2013b: Fig. 401) ............. S. grandimaculatus Benick

- Elytral spot smaller, about 1/3 as long as one elytron. Aedeagus as Figs. 15 & 16 A. Spermatheca as Figs. 15 & 16 H............................................................................................... S . oculifer Puthz

15. Punctation of tergite VII denser, interstices about as wide as diameter of punctures. Aedeagus as Figs. 3 E & 4 A. Spermatheca as Figs. 3 I & 4 H...................................................... S . zhangyejunianus Lv et Zhou, sp. nov

- Punctation of tergite VII sparser, interstices much wider than diameter of punctures. Aedeagus as Figs. 23 & 24 A............................................................................................ S . tenuimargo Cameron