Arthromelodes Jeannel, 1954

Chinese common name: njà甲¤

Arthromelodes Jeannel, 1954b: 247; Jeannel 1957 (correction of the locality of the type species); Nomura 1991 (description, new generic synonym, key to Japanese species); Yin 2018c (first country record in China). Type species: Arthromelodes cariei Jeannel, 1954b: 248 (original designation).

= Pseudobatriscenus Jeannel, 1958: 66. Type species: Batrisocenus dilatatus Raffray, 1909: 25 (original designation). Synonymized by Nomura 1991: 337.

= Plocamarthrus Jeannel, 1960: 423. Type species: Plocamarthrus championi Jeannel, 1960: 423 (original designation). syn. nov.

The genus Arthromelodes previously comprised 21 species distributed in Japan (Nomura 1991), China (Yin 2018c), Vietnam (Nomura & Pham 2019), Laos (Jeannel 1957), and Myanmar (Nomura & Aung 2020), and is strongly diversified in East to Southeast Asia and along the Himalaya. There is no determined synapomorphy that links all included species, but members share a large basal capsule and erect dorsal lobe of the aedeagus. Plocamarthrus with four species distributed in northern India has a more elongate ventral stalk of the median lobe, and an elongate and apically strongly curved dorsal lobe of the aedeagus. Otherwise, the genus cannot be effectively separated from Arthromelodes by external morphology. Here, Arthromelodes is proposed as a junior synonym of Plocamarthrus, with the former being the older name, syn. nov. The synonymy creates the following new combinations: Arthromelodes championi (Jeannel, 1960), comb. nov., A. cameroni (Jeannel, 1960), comb. nov., A. planiceps (Jeannel, 1960), comb. nov., and A. abdominalis (Jeannel, 1960), comb. nov. Nomura (1991: 338) was the first to point out the morphological similarity between these two genera, and one of the new species described here is named in his honor.

Twenty-six new species from Tibet are described in this paper, and A. championi (Jeannel) is recorded from China (in Tibet) for the first time. The 27 Tibetan species are keyed below.

Key to Tibetan species of Arthromelodes (male)

1 Sexual characters present on antenna or tergites............................................................. 2

- Antenna or tergites lacking sexual characters.............................................................. 23

2 Sexual characters present on antenna...................................................................... 3

- Sexual characters present on tergites...................................................................... 7

3 Antennomeres 9 and 10 with dense, short setae.............................................................. 4

- Antennomeres 9 and 10 normally setose................................................................... 5

4 Vertex with distinct median longitudinal sulcus (Fig. 7B); antennomere 7 small, unmodified; metaventrite densely setose (Fig. 9D).............................................................................. A. crassicornis sp. nov.

- Vertex lacking median longitudinal sulcus (Fig. 18B); antennomere 7 enlarged (Fig. 18C); metaventrite lacking dense setae......................................................................................... A. lebus sp. nov.

5 Antennal modification presents on antennomere 11 (Fig. 8C); mesotibia with markedly large apical spine (Fig. 8E)................................................................................................ A. cona sp. nov.

- Antennal modification present on antennomere 9; mesotibia lacking or with small apical spine........................ 6

6 Antennomere 7 mesally expanded (Fig. 6C); elytra truncate at bases (Fig. 6A); mesotibia with triangular apical spine (Fig. 6D)............................................................................... A. championi (Jeannel)

- Antennomere 7 apically projecting on anterolateral margin (Fig. 25C); elytra constricted at bases (Fig. 25A); mesotibia lacking apical spine.......................................................................... A. speciosus sp. nov.

7 Mesofemur with protuberance or spine on ventral margin...................................................... 8

- Mesofemur lacking protuberance or spine on ventral margin................................................... 9

8 Elytra constricted at bases (Fig. 13A); ventral spine of mesotrochanter asetose (Fig. 13C); mesotibia with small apical tubercle; tergites 1–4 (IV–VII) modified (Fig. 13D)................................................... A. gyamda sp. nov.

- Elytra truncate at bases (Fig. 21A); ventral spine of mesotrochanter setose (Fig. 21C); mesotibia with large, curved apical spine (Fig. 21D); only tergite 1 (IV) modified (Fig. 21E)............................................. A. monba sp. nov.

9 Metafemur distinctly thickened distally................................................................... 10

- Metafemur normally formed, not distinctly thickened distally................................................. 11

10 Vertex with long, distinct median carina (Fig. 11B); abdomen slightly longer than wide due to elongate tergite 1 (IV) (Fig. 11A); tergite 1 (IV) lacking setose patches lateral to central cavity (Fig. 11D).......................... A. cylindricus sp. nov.

- Vertex with short, indistinct median carina (Fig. 20B); abdomen much wider than long (Fig. 20A); tergite 1 (IV) with setose patches lateral to central cavity (Fig. 20D)................................................... A. markam sp. nov.

11 Tergite 1 (IV) lacking central cavity or impression.......................................................... 12

- Tergite 1 (IV) with central cavity........................................................................ 17

12 Body bicolored, with black head, pronotum and abdomen black, elytra reddish-brown (Fig. 5A); tergite 1 (IV) with median projection at posterior margin (Fig. 5D)...................................................... A. bicolor sp. nov.

- Body unicolorous, reddish-brown; tergite 1 (IV) lacking median projection at posterior margin....................... 13

13 Tergite 5 (VIII) modified, with broad and deep basal cavity (Fig. 24D)........................ A. songxiaobini sp. nov.

- Tergite 5 (VIII) simple, unmodified...................................................................... 14

14 Protibia with angulate protuberance at lateral margin near apex (Fig. 28C)..................... A. zhentangensis sp. nov.

- Protibia lacking protuberance at lateral margin.............................................................. 15

15 Mesotrochanter with long bunch of setae on ventral margin (Fig. 16C); mesotibia with tiny tubercle at apex (Fig. 16D)......................................................................................... A. langjicuo sp. nov.

- Mesotrochanter with short setose protuberance on ventral margin; mesotibia with moderately large tubercle at apex...... 16

16 Median projection of tergite 1 (IV) with two widely separated posterolateral angles (Fig. 2E)........... A. alpitorus sp. nov.

- Median projection of tergite 1 (IV) with single posterior or narrowly separated posterolateral angles (Fig. 26E)................................................................................................... A. torus sp. nov.

17 Lateral margin of tergite 1 (IV) angulate (Fig. 3D)............................................ A. angulatus sp. nov.

- Lateral margin of tergite 1 (IV) smooth................................................................... 18

18 Pronotum with exceptionally elongate and erect setae at lateral margin.......................................... 19

- Pronotum normally setose, lacking exceptionally elongate setae at lateral margin.................................. 20

19 Body length over 2.6 mm; vertex with complete reversed U-shaped sulcus connecting foveae (Fig. 12B); antennomeres distinctly elongate (Fig. 12A).............................................................. A. flosculus sp. nov.

- Body length less than 1.8 mm; vertexal sulcus incomplete (Fig. 19B); antennomeres slightly elongate (Fig. 19A).................................................................................................. A. lotus sp. nov.

20 Protibia distinctly expanded (Fig. 15A)........................................................ A. lage sp. nov.

- Protibia slender, not expanded.......................................................................... 21

21 Lateral and posterior margins of elytra densely setose (Fig. 14A); antennomeres distinctly elongate (Fig. 14A); central cavity of tergite 1 (IV) exceptionally large (Fig. 14E)............................................... A. intricatus sp. nov.

- Lateral and posterior margins of elytra lacking dense setae; antennomeres moderately elongate; central cavity of tergite 1 (IV) relatively much smaller............................................................................... 22

22 Mesotibia with tiny apical tubercle; tergite 1 (IV) with single central cavity, lacking tubercle or projection (Fig. 4D)............................................................................................. A. aniqiao sp. nov.

- Mesotibia with distinct apical spur; tergite 1 (IV) with median projection anterior to and large tubercle posterior to central cavity (Fig. 7F)......................................................................... A. complexus sp. nov.

23 Vertex with dense, exceptionally long setae (Fig. 10B)......................................... A. criniger sp. nov.

- Vertex normally setose, lacking dense, long setae........................................................... 24

24 Body bicolored (Fig. 22A); protibia strongly sinuate (Fig. 22D)............................... A. nepaeformis sp. nov.

- Body unicolorous; protibia slightly curved or nearly straight.................................................. 25

25 Lateral margin of pronotum normally rounded, not expanded (Fig. 23A); mesotibia moderately expanded mesally at basal fourth, with small apical projection (Fig. 23C)................................................ A. nomurai sp. nov.

- Lateral margin of pronotum moderately to strongly expanded; mesotibia not expanded mesally at basal fourth, with large apical spine.............................................................................................. 26

26 Lateral margin of pronotum strongly expanded (Fig. 17B); apical spine of mesotibia curved (Fig. 17D); ventral stalk of median lobe moderately broad at apex in dorsoventral view (Fig. 17F, H)................................ A. latithorax sp. nov.

- Lateral margin of pronotum moderately expanded (Fig. 27B); apical spine of mesotibia straight (Fig. 27D); ventral stalk of median lobe strongly broad at apex in dorsoventral view (Fig. 27G).............................. A. zhangmu sp. nov.