Key to the species of China Opalimosina (males)

1. An additional small inclinate setula present between inner occipital bristles and outer occipital bristles; mid femur basally with a group of setae (Roháček, 1985, Fig. 983); hind tibia without ventral preapical spur; S5 posteromedially with a large oval area, densely covered by small blunt cuticular projections (Roháček, 1985, Fig. 1001)...................... O. czernyi (Duda)

-. No additional setula between inner occipital bristles and outer occipital bristles; mid femur simply finely setulose; hind tibia with distinct ventral preapical spur; S5 with paired posteromedial processes or spinose region or small patches........... 2

2. Sternite 5 with pair of long and ventrally curved posteromedial processes (Figs. 2D, 6D)............................. 3

-. Sternite 5 with paired short and straight posteromedial processes or spiny region or small patches (Deng et al., 2019, Fig. 5; Figs. 4B, 8D; Hayashi, 1989, Fig. 4; Roháček, 1985, Fig. 1034; Su et al., 2013, Figs. 1g, 2f).......................... 4

3. Sternite 5 with two clusters of robust spines between bases of posteromedial processes (Fig. 2D); hind tibia with a long curved long ventral preapical spur (Fig. 1C); posterior corner of surstylus with 1 long and robust bristle and 2 thinner setae (Fig. 2C); cercus with a long seta at posterodorsal margin(Fig. 2A)....................................... O. aculeata sp. nov.

-. Sternite 5 with a series of short setae between bases of processes (Fig. 6D); hind tibia with a very short, straight ventral preapical spur (Fig. 5D); posterior corner of surstylus with 2 robust (1 dorsal and 1 ventral) bristles (Figs. 6B, 6C); cercus with a short, stout and blunt medioventral spine (Fig. 6A)........................................... O. setifera sp. nov.

4. C ending at R4+5..................................................................................... 5

-. C continuing distinctly beyond apex of R4+5............................................................... 8

5. Sternite 5 entirely sclerotized, posteromedially with two comb-like processes with setulae above, with two warts at base of processes and a row of small setae around warts anteriorly (Deng et al., 2019, Fig. 5)..................... O. verruca Su

-. Sternite 5 with membranous region, posteromedially with processes or small patches or dense small spines, without warts (Figs. 4B, 8D; Hayashi, 1989, Fig. 4)........................................................................... 6

6. Sternite 5 with a longitudinally membranous region separating left and right halves; posterior margin of each part densely covered with small spines (Hayashi, 1989, Fig. 4)....................................... O. pseudomirabilis Hayashi

-. Sternite 5 with two characteristic processes or small patches posteriorly and a weakly sclerotized area centrally, never longitudinally divided (Figs. 4B, 8D)...................................................................... 7

7. Sternite 5 posteromedially incised distinctly, with a pair of posterior processes at sides of incision and a weakly sclerotized, irregular area centrally (Fig. 4B), otherwise very densely and shortly setulose; epandrium with short sparse setulae (Fig. 4A); postgonite relatively straight (Fig. 4D)................................................. O. calcarifera (Roháček)

-. Sternite 5 posteromedially incised weakly, with two small patches posteriorly and a weakly sclerotized, semicircular area centrally (Fig. 8D); postgonite sinuate (Fig. 8E)............................................ O. spathulata Hayashi

8. Sternite 5 with an arc-shaped membranous stripe separating posteromedial part from anterior part, posteromedial part with densely long setose patches laterally and with a pair of cuticular structures on posterior margin (Roháček, 1985, Fig. 1034); surstylus with 2 robust long setae and 1 smaller one at posterior corner (Roháček, 1985, Fig. 1031)..... O. mirabilis (Collin)

-. Sternite 5 with a deep and narrow incision or intact posteromedially (Su et al., 2013, Figs. 1g, 2f); surstylus with 2 robust long setae at posterior corner (Su et al., 2013, Figs. 1f, 2d)......................................................... 9

9. Sternite 5 with a deep and narrow incision posteromedially, a narrow membranous region centrally with a posterior row of robust setae, a dense row of spines at each side of incision and a setulose projection lateral to the row of spines (Su et al., 2013, Fig. 1g); postgonite sinuate and apex pointed................................................. O. differentialis Su

-. Sternite 5 posteromedially simple, with two small comb-like processes with setulae above, a dark arc-shaped stripe between processes and a row of long setae around stripe anteriorly (Su et al., 2013, Fig. 2f); postgonite with narrow and digitiform apex (Su et al., 2013, Fig. 2c).................................................................. O. prominentia Su