A key to Chinese species of the genus Hydrochara Berthold

1. Prosternum with a long acute spine posteriorly...................................... H. dichroma (Fairmaire, 1892)

- Prosternum without long acute spine posteriorly............................................................. 2

2. Lateral rim of elytra relatively wide, wider than diameter of the serial punctures near base of elytron. Legs reddish black to black............................................................................................... 3

- Lateral rim of elytra narrow, not wider than diameter of the serial punctures near base of elytron. Legs yellowish to reddish brown.............................................................................................. 4

3. Maxillary palps yellowish to reddish brown, not paler at the apical portion of each segment (Fig. 4A). Intervals of systematic punctures with 1–2 rows of vaguely impressed fine punctures (Fig. 4C). Aedeagus with lateral margins of parameres straight medially; gonopore oval (Fig. 3C). Body length 21.5–23.5 mm .................................... H. loong sp. nov.

- Maxillary palps dark piceous with apical portion of each segment slightly paler (Fig. 4B). Intervals of systematic punctures with 1–2 distinct rows of fine punctures (Fig. 4D). Aedeagus with lateral margins of parameres sinuate or slightly concave medially; gonopore triangular (Fig. 3D). Body length 14.0–17.5...................................... H. libera (Sharp, 1884)

4. Parameres of aedeagus with apices angulately produced inwards. Body length 12.5–18 mm ........ H. affinis (Sharp, 1873)

- Parameres of aedeagus with apices not angulately produced inwards. Body length 11.0– 16.5 mm .. H. flavipes (Steven, 1808)