Key to Syndicus species of China

1 Base of antennomere XI nearly as broad as apex of antennomere X; antennomere XI shorter than half length of antennomere X (subgenus Syndicus)................................................................................... 2

- Base of antennomere XI much narrower than apex of X; antennomere XI longer than half length of antennomere X (subgenus Semisyndicus)....................................................................................... 4

2 Body length exceeding 4 mm (Yin et al. 2014: fig. 1). (Zhejiang, Fujian, Hunan, Guangdong).............. S. jaloszynskii

- Body length less than 4 mm ............................................................................ 3

3 Body length less than 2.7 mm, each elytron with marginal impression on sides of elytra (Yin & Zhou 2015: figs 1A, 4A). (Hainan)...................................................................................... S. qiong

- Body length no less than 2.9 mm, each elytron lacking marginal impression. (Yunnan).................. S. himalayanus

4 Pronotal disc glossy, without well-marked punctures (Yin & Li 2015: fig. 1B). (Hainan).................. S. hainanicus

- Pronotal disc with coarse, sharply marked punctures........................................................ 5

5 Body length less than 2.5 mm (Yin & Li 2015: fig. 1A). (Hainan)................................ S. grossepunctatus

- Body length exceeding 2.5 mm ......................................................................... 6

6 Pronotal disc relatively sparsely punctate (Yin & Zhou 2016: fig. 5A). (Yunnan).......................... S. sinensis

- Pronotal disc relatively densely punctate (Fig. 5A; Yin & Zhou 2016: fig. 5D).................................... 7

7 Body length 3.21 mm, endophallus with a C-sharped sclerite (Fig. 4 B). (Yunnan)........................ S. long sp. n.

- Body length 3.02–3.05 mm, endophallus without a C-shaped sclerite (Jałoszyński 2008: fig. 3). (Sichuan)... S. sichuanicus