Taxonomic revision of the species of Stenothemus from Southwest China (Coleoptera, Cantharidae), with the descriptions of five new species

The species of Stenothemus Bourgeois, 1907 from Southwest China are reviewed. Three species are transferred to this genus, S. davidi (Pic, 1926) comb. nov. (from Malthacus Kirby, 1837), S. minutissimus (Pic, 1933) comb. nov. (from Micropodabrus Pic, 1920) and S. singularicollis (Pic, 1933) comb. nov. (from Lycocerus Gorham, 1895). Two new synonyms are suggested, S. dinshuiensis Švihla, 2011 syn. nov. is synonymized with S. davidi and S. melleus Švihla, 2005 syn. nov. with S. singularicollis. Stenothemus shaanxiensis Švihla, 2004 stat. nov. is raised to species level from a subspecies of S. benesi Švihla, 2004. Five new species are described, S. gracilis Y. Yang & X. Yang sp. nov., S. chongqingensis Y. Yang & H. Liu sp. nov., S. flavicollis Y. Yang & S. Ge sp. nov., S. jindraimimus Y. Yang & X. Yang sp. nov. and S. laticornis Y. Yang & H. Liu sp. nov., which are illustrated with photographs of habitus, aedeagi, abdominal sternites VIII and internal genitalia of the female. Characters of the female reproductive system are described for the first time for the following species: S. diffusus Wittmer, 1974, S. dundai Švihla, 2004, S. grahami Wittmer, 1974, S. jindrai Švihla, 2004, S. tryznai Švihla, 2004 and S. singularicollis. Some additional distribution information is added for previously known species. A key for the identification of all studied species is provided.

Male (Fig. 1B) AedeAgus ( Fig. 2A-C). Moderately swollen dorsally at basal part, moderately reduced basally in diameter; basal piece nearly as long as dorsal plate of each paramere, with a large, bifurcate conjoined middle nodule at base of ventral side; ventral processes of parameres nearly parallel to each other, long and slightly widened apically, nearly straight in lateral view; dorsal plate nearly as long as ventral process, evenly narrowed apically and next to each other, apex rounded and folded ventrally; apical parts of laterophyses depressed and approaching each other, apex acute and directed dorsally, slightly exceeding middle emargination between dorsal plates.

Female
AbdominAl sternite Viii (Fig. 3A). Obliquely narrowed posteriorly, lateroapical angles obtusely rectangular, posterior margin deeply and triangularly emarginate in middle and feebly sinuate on both sides, behind the notch with a membrane which is moderately sclerotized and triangularly bilobed at apex.
internAl orgAn of reproductiVe system (Fig. 4A). Vagina stout, with median oviduct situated at ventroapical part, vagina abruptly narrowed in apical part and extended into a long duct which diverticulum and spermathecal duct are arising from; diverticulum relatively short, about 0.33 times adult body length, evenly thinned apically, slender tube-shaped and spiral; spermathecal duct much shorter than diverticulum; spermatheca slender, tube-shaped and spiral, clearly thinner than spermathecal duct and slightly shorter than diverticulum, with basal part extended into a short tube, at opening of accessory gland. Accessory gland thin in basal part and the remainder moderately thin, nearly as long as spermatheca.

Remarks
In the original publication (Švihla 2004), this species was treated as a subspecies of S. benesi. However, differences between the two taxa are found not only in the external appearance, but also in the structures of the aedeagus. In S. shaanxiensis, the body is smaller and yellow (Fig. 1B), aedeagus  with the dorsal plate of each paramere approaching that of the other, and the ventral process of each paramere distinctly thickened apically. In contrast, in S. benesi, the body is larger and brown (Fig. 1A), aedeagus (Švihla 2004: figs 161-163) with dorsal plates of parameres separated from each other and ventral process of each paramere slightly thickened apically. These differences are sufficient to support their independent status, so it is proposed that S. shaanxiensis is separated from S. benesi and upgraded to the specific level. The dorsal and ventral view of the aedeagus and the female reproductive system for this species are described and illustrated for the first time. (Pic, 1926)
Male AedeAgus (Fig. 2D-F). Moderately swollen laterally at basal part, moderately reduced apically in diameter; basal piece nearly as long as dorsal plate of each paramere, with a small, bifurcate conjoined middle nodule at base of ventral side; ventral processes of parameres nearly parallel to each other, moderately long and slightly thickened apically, bent ventrally in lateral view; dorsal plates slightly longer than ventral processes, strongly narrowed near base and approaching each other, apex acute and directed ventrally; apical parts of laterophyses depressed and separated from each other, apex acute and bent dorsally, roughly reaching middle emargination between dorsal plates. Female (Fig. 1C) AbdominAl sternite Viii (Fig. 3B). Moderately narrowed posteriorly, lateroapical angles widely rounded, posterior margin widely and roundly emarginate in middle and feebly sinuate on both sides, behind the notch with a membrane which is sclerotized and triangularly bilobed at apex. internAl orgAn of reproductiVe system (Fig. 4B). Vagina stout, with median oviduct situated at ventroapical part, vagina abruptly narrowed in apical part and extended into a short duct which diverticulum and spermathecal duct are arising from; diverticulum moderately long, about 0.85 times adult body length, evenly thinned apically, slender tube-shaped and spiral; spermathecal duct slightly long but much shorter than diverticulum; spermatheca slender tube-shaped and spiral, obviously thinner than spermathecal duct and slightly shorter than diverticulum, with basal part extended into a short tube, at opening of accessory gland. Accessory gland thin in basal part and the remaining parts thick, much shorter than spermatheca.

Remarks
The type (Fig. 1C) is seriously damaged, with right antenna, all legs except the left proleg one and abdomen missing, and with "alle Klauen einfach" ['all claws simple'] label attached, written by Dr W. Wittmer. Fortunately, some additional material including males and females was available, enabling us to recognize it. The genitalia of both sexes are illustrated and described for the first time. Based on the structure of the aedeagus (Fig. 2D-F) and all simple claws, it definitely belongs to Stenothemus. Furthermore, no difference is found from S. dinshuiensis, including overall appearance and structure of aedeagus, so it is considered to be a junior synonym of S. davidi.  Švihla, 2004 stat. nov. (IZAS, Shaanxi). B. S. davidi (Pic, 1926) comb. nov. (IZAS, Shaanxi). C. S. diffusus Wittmer, 1974 (MHBU, Sichuan). D. S. dundai Švihla, 2004 (MHBU, Sichuan). Abbreviations: see Material and methods. Scale bars = 0.5 mm. Wittmer, 1974 Figs 1D, 2G-I, 3C, 4C

Descriptive notes
Body length (both sexes): 10.0-12.8 mm; width: 2.1-3.0 mm. (Fig. 1D) AedeAgus ( Fig. 2G-I). Strongly swollen dorsally in basal part, diameter decreased apically; basal piece slightly shorter than dorsal plate of each paramere, with a large, bifurcate conjoined middle nodule at base of ventral side; ventral processes of parameres nearly parallel to each other, long and slightly thickened apically; dorsal plate slightly shorter than ventral process, evenly narrowed apically, layering in middle, external layer roundly emarginate in middle, internal layer deeply and triangularly emarginate, rounded at apex; apical parts of laterophyses compressed and next to each other, apex rounded and bent dorsally, slightly exceeding middle emargination between dorsal plates.

Female
AbdominAl sternite Viii (Fig. 3C). Obliquely narrowed posteriorly, lateroapical angles widely triangular, posterior margin shallowly and triangularly emarginate in the middle, and weakly sinuate on both sides. internAl orgAn of reproductiVe system (Fig. 4C). Vagina elongate, with median oviduct situated at ventroapical part, vagina abruptly narrowed in apical part and extended into a short duct which diverticulum and spermathecal duct are arising from; diverticulum moderately long, about 0.35 times adult body length, evenly thinned apically, slender tube-shaped and spiral; spermathecal duct slightly longer than diverticulum; spermatheca slender tube-shaped and spiral, thinner than spermathecal duct and nearly as long as diverticulum, with basal part extended into a short tube, at opening of accessory gland. Accessory gland thin and nearly as long as spermatheca.

Remarks
The dorsal and lateral views of aedeagus and the female reproductive system are described and illustrated for the first time. Švihla, 2004 Figs 1E, 3D, 4D
internAl orgAn of reproductiVe system (Fig. 4D). Vagina elongate, with median oviduct situated at ventroapical part, vagina abruptly narrowed in apical part and extended into a short duct which diverticulum and spermathecal duct are arising from; diverticulum relatively short, about 0.36 times adult body length, evenly thinned apically, slender tube-shaped and spiral; spermathecal duct slightly long but much shorter than diverticulum; spermatheca slender tube-shaped and spiral, obviously thinner than spermathecal duct and much longer than diverticulum, with basal part extended into a short tube, where accessory gland opens. Accessory gland thin and slightly shorter than spermatheca.

Remarks
The female reproductive system is illustrated and described for the first time. Wittmer, 1974 Figs 1F, 3E, 6A-C, 8A

Stenothemus grahami
Stenothemus grahami Wittmer, 1974: 60, fig. 18. Strongly swollen dorsally at basal part, moderately reduced apically in diameter; basal piece slightly shorter than dorsal plate of each paramere, with a large, bifurcate conjoined middle nodule at base of ventral side; ventral processes of parameres nearly parallel to each other, moderately long and slightly narrowed apically, bent dorsally in lateral view; dorsal plate obviously longer than ventral process, evenly narrowed apically, apex rounded, outer margins folded ventrally; apical parts of laterophyses compressed and next to each other, apex acute and directed laterally, distinctly exceeding emargination between dorsal plates.
internAl orgAn of reproductiVe system (Fig. 8A). Vagina elongate, with median oviduct situated at ventroapical part, vagina abruptly narrowed in apical part and extended into a long duct which diverticulum and spermathecal duct are arising from; diverticulum relatively short, about 0.29 times adult body length, evenly thinned apically, slender tube-shaped and spiral; spermathecal duct slightly long but much shorter than diverticulum; spermatheca slender tube-shaped and spiral, obviously thinner than spermathecal duct and much longer than diverticulum, with basal part extended into a short tube, at opening of accessory gland. Accessory gland thin in basal part and the remainder moderately thin, nearly as long as spermatheca.

Remarks
The female reproductive system and dorsal and lateral views of the aedeagus for this species are described and illustrated for the first time. Švihla, 2004 Figs 3F, 5A, 8B
internAl orgAn of reproductiVe system (Fig. 8B). Vagina stout, with median oviduct situated at ventroapical part, vagina abruptly narrowed in apical part and extended into a short duct which diverticulum and spermathecal duct are arising from; diverticulum relatively short, about 0.32 times adult body length, evenly thinned apically, slender tube-shaped and spiral; spermathecal duct slightly long but much shorter than diverticulum; spermatheca slender tube-shaped and spiral, obviously thinner than spermathecal duct and slightly longer than diverticulum, with basal part extended into a short tube, at opening of accessory gland. Accessory gland thin in basal part and the remainder moderately thin, slightly shorter than spermatheca.  (Pic, 1933) comb. nov., holotype, ♂ (MNHN). C. S. tryznai Švihla, 2004, holotype, ♂ (NMPC). D. S. singularicollis (Pic, 1933) comb. nov., holotype, ♀ (NHMH). E. S. melleus Švihla, 2005 syn. nov., holotype, ♂ (= S. singularicollis) (NMPC). Scale bars = 1.0 mm. times as long as II, IV-XI each with a small and smooth longitudinal impression in middle of outer edge, VII longest, XI slightly longer than X, pointed at apex.
pronotum. Subquadrate, about 1.1 times as long as wide, anterior margin nearly straight, anterior angles obtuse, widely truncate, lateral margins narrowed posteriorly, and slightly sinuate, posterior margin slightly sinuate, posterior angles obtuse, slightly protruding, disc distinctly convex on posterolateral parts, surface finely and densely punctate.
elytrA. Nearly parallel-sided, about 3.6 times as long as humeral width, 4.6 times longer than pronotum, surface finely and densely punctate, present with hardly visible longitudinal costae.
AedeAgus (Fig. 6D-F). Strongly swollen laterally at basal part, apically reduced in diameter; basal piece slightly shorter than dorsal plate of each paramere, with a moderately large, bifurcate conjoined middle nodule at base of ventral side; ventral processes of parameres nearly parallel to each other, short and distinctly thickened apically; dorsal plates of parameres conjoined, with a rounded emargination in the middle of the apical margin, distinctly longer than the ventral process, apex rounded, with a pair of protuberances on inner surface; apical part of laterophyses depressed and separated from each other, apex acute, not reaching middle emargination between dorsal plates.

Female
Similar to male, but body stouter, eyes small, less protruding, head width across eyes 1.2 times as wide as pronotum, antennae shorter and extending to elytral mid-length, IV-XI without impressions; elytra about 3.0 times as long as humeral width.
AbdominAl sternite Viii (Fig. 7A). Moderately narrowed posteriorly, lateroapical angles obtusely triangular and protruding, posterior margin shallowly and triangularly emarginate in middle and slightly sinuate on both sides; behind the notch with a membrane, which is sclerotized and triangularly bilobed at apex. internAl orgAn of reproductiVe system (Fig. 8C). Vagina stout, with median oviduct situated at ventroapical part, vagina abruptly narrowed in apical part and extended into a short duct which diverticulum and spermathecal duct are arising from; diverticulum relatively short, about 0.41 times adult body length, evenly thinned apically, slender tube-shaped and spiral; spermathecal duct slightly long but much shorter than diverticulum; spermatheca slender tube-shaped and spiral, obviously thinner than spermathecal duct and slightly longer than diverticulum, with basal part extended into a short tube, at opening of accessory gland. Accessory gland thin and slightly shorter than spermatheca.

Distribution
China (Gansu, Sichuan). New record for Sichuan Province.

Remarks
Having examined the type, and some additional specimens available, we redescribe this little-known species. Based on the structure of the aedeagus and all simple claws, it should be placed in Stenothemus. Švihla, 2004 Figs 5C, 7B, 8D
internAl orgAn of reproductiVe system (Fig. 8D). Vagina elongate, with median oviduct situated at ventroapical part, vagina abruptly narrowed in apical part and extended into a short duct which diverticulum and spermathecal duct are arising from; diverticulum relatively short, about 0.32 times adult body length, evenly thinned apically, slender tube-shaped and spiral; spermathecal duct much shorter than diverticulum; spermatheca slender tube-shaped and spiral, obviously thinner than spermathecal duct and nearly as long as diverticulum, with basal part extended into a slightly long tube, at opening of accessory gland. Accessory gland thin and much longer than spermatheca.

Remarks
The female reproductive system of this species is illustrated and described for the first time. (Pic, 1933)

Female
AbdominAl sternite Viii (Fig. 7C). Moderately narrowed posteriorly, lateroapical angles obtusely rounded, posterior margin widely and roundly emarginate in middle and feebly sinuate on both sides, behind the notch with a membrane which is sclerotized and triangularly bilobed at apex.
internAl orgAn of reproductiVe system (Fig. 12A). Vagina stout, with median oviduct situated at ventroapical part, vagina abruptly narrowed in apical part and extended into a short duct which diverticulum and spermathecal duct are arising from; diverticulum extremely long, about 0.58 times adult body length, evenly thinned apically, slender tube-shaped and spiral; spermathecal duct long but much shorter than diverticulum; spermatheca slender tube-shaped and spiral, thinner than spermathecal duct and nearly as long as diverticulum, with basal part extended into a short tube, where accessory gland opens. Accessory gland thin in basal part, and the remainder moderately thin, much shorter than spermatheca.

Remarks
Having examined the holotypes of Podabrinus singularicollis (Fig. 5D) and Stenothemus melleus (Fig. 5E), as well as a large series of additional specimens available, we are unable to find differences justifying their separation, which has led us to consider all the examined specimens to be conspecific. Therefore, we suggest the latter species should be synonymized with the former, which should be called S. singularicollis according to the structure of the aedeagus and simple claws. Additionally, the female reproductive system and abdominal sternite VIII of this species are described for the first time.

Differential diagnosis
This new species is most similar to S. limbatipennis (Pic, 1926), but can be distinguished by the following characters: antennomeres IV-XI each with a small oval impression in middle of outer edge in male (with longitudinal impressions in S. limbatipennis); pronotum about 1.3 times as long as wide (while nearly as long as wide in S. limbatipennis); aedeagus: ventral process of each paramere moderately bent ventrally in lateral view, middle emargination between dorsal plates longer than half its length, laterophyses clearly exceeding middle emargination (while ventral process strongly bent ventrally, middle emargination between dorsal plates shorter, apex of laterophyses just reaching in S. limbatipennis, see Yang et al. 2021: figs 3g-i); abdominal sternite VIII: lateroapical angles triangular and protruding, posterior margin rectangularly emarginate in middle, membrane strongly sclerotized and triangularly bilobed at apex (lateroapical angles widely rounded, middle emargination rounded, membrane weakly sclerotized and tapered at apex in S. limbatipennis, see Yang et al. 2021: fig. 8c); female internal organ of reproductive system: diverticulum obviously longer than spermatheca (while shorter in S. limbatipennis, see Yang et al. 2021: fig. 6c).

Etymology
The specific name is derived from the Latin 'gracilis' ('slender'), referring to its slender body. HeAd. Subquadrate, surface densely and finely punctate, each side with a smooth and rectangular impression behind antennal socket; eyes strongly protruding, head width across eyes 1.6 times wider than pronotum; terminal maxillary palpomeres long-triangular, widest in middle; antennae filiform, extending to ¾ length of elytra, antennomeres II about twice times as long as wide at apices, III about 1.8 times longer than II, IV-XI each with a small and smooth oval impression in middle of outer edge, VII longest, XI slightly longer than X, pointed at apex.

Holotype
pronotum. Subquadrate, about 1.3 times as long as wide, anterior margin slightly arcuate, anterior angles obtuse, sub-rectangular, lateral margins nearly parallel and slightly sinuate, posterior margin slightly arcuate and narrowly bordered, posterior angles sub-rectangular, disc distinctly convex on posterolateral parts, surface finely and densely punctate. elytrA. Nearly parallel-sided, about 3.8 times as long as humeral width, 4.9 times longer than pronotum, surface finely and densely punctate, with hardly visible longitudinal costae present. AedeAgus (Fig. 6G-I). Moderately swollen laterally in basal part, reduced apically in diameter; basal piece nearly as long as dorsal plate of each paramere, with a small, bifurcate conjoined middle nodule at base of ventral side; ventral processes of parameres approaching each other, short and slightly thickened apically, bent ventrally in lateral view; dorsal plates slightly longer than ventral processes, strongly narrowed near base, approaching each other, apex acute and directed ventrally; apical parts of laterophyses depressed and separated from each other, apex rounded and bent dorsally, clearly exceeding middle emargination between dorsal plates.

Female
Similar to male, but body stouter than male, eyes small, less protruding, head width across eyes 1.2 times wider than pronotum, antennae shorter and roughly extending to elytral mid-length, IV-XI without smooth oval impressions; pronotum wider, nearly as long as wide; elytra about 3.3 times as long as humeral width.
AbdominAl sternite Viii (Fig. 7D). Strongly narrowed posteriorly, lateroapical angles triangular and protruding, posterior margin widely and rectangularly emarginate in middle and feebly sinuate on both sides, behind the notch with a membrane which is sclerotized and triangularly bilobed at apex, with a rectangular sclerite present at center and a small longitudinal sclerite on each side.
internAl orgAn of reproductiVe system (Fig. 12B). Vagina stout, with median oviduct situated at ventroapical part, vagina abruptly narrowed in apical part and extended into a short duct which diverticulum and spermathecal duct are arising from; diverticulum extremely long, about 0.86 times adult body length, evenly thinned apically, slender tube-shaped and spiral; spermathecal duct much shorter than diverticulum; spermatheca slender tube-shaped and spiral, obviously thinner than spermathecal duct and much shorter than diverticulum, with basal part extended into a short tube, at opening of accessory gland. Accessory gland thin in basal part and the remainder thick, obviously shorter than spermatheca.

Variation within species
Head sometimes with yellow markings behind eyes, pronotum more or less lightened on posterolateral parts, elytra sometimes yellow at humeri and bases of outer margins.

Differential diagnosis
Similar to S. laticornis Y. Yang & H. Liu sp. nov., but differs in the following characters: male antennomeres IV-XI cylindrically thickened and each with a small and smooth longitudinal impression in middle of outer edge (while flattened and with oval impressions in S. laticornis sp. nov.); aedeagus: ventral process of each paramere slightly narrowed apically, bent ventrally in lateral view, apices of laterophyses not reaching middle emargination between dorsal plates (while ventral process distinctly thickened and bent dorsally in the S. laticornis sp. nov., and laterophyses exceeding middle emargination in S. laticornis sp. nov. (Fig. 11A-C)).

Etymology
The specific name is derived from the name of the type locality, Chongqing, China. Male (Fig. 9B) colorAtion. Body brown, head, elytra black, with an orange marking at vertex, pronotum and scutellum testaceous, pronotum more or less lightened at anterior angles, prosternum, coxae and bases of inner margins of femora yellow. Body densely covered with short, semi-recumbent pale pubescence.
HeAd. Subquadrate, surface densely and finely punctate, each side with a smooth and rectangular impression behind antennal socket; eyes large, strongly protruding, head width across eyes 1.4 times as wide as pronotum; terminal maxillary palpomeres long-triangular, widest in middle; antennae filiform, almost reaching apices of elytra, antennomeres II about 1.5 times as long as wide at apices, III about 2.3 times longer than II, IV-XI cylindrically thickened and each with a small and smooth longitudinal impression in middle of outer edge, IV widest, V to XI gradually narrowing towards apex, XI slightly longer than X, pointed at apex.
pronotum. Subquadrate, about 1.2 times as long as wide, anterior margin arcuate, anterior angles obtuse, sub-rectangular, lateral margins slightly sinuate, posterior margin slightly sinuate and narrowly bordered, posterior angles sub-rectangular, disc strongly convex on posterolateral parts, surface finely and densely punctate.
elytrA. Nearly parallel-sided, about 3.5 times as long as humeral width, 4.4 times longer than pronotum, surface finely and densely punctate, with hardly visible longitudinal costae.
AedeAgus (Fig. 10A-C). Moderately swollen laterally at basal part, strongly reduced in diameter apically; basal piece nearly as long as dorsal plate of each paramere, with a large, bifurcate conjoined middle nodule at base of ventral side; ventral processes parameres approaching each other, short and slightly narrowed apically, bent ventrally in lateral view; dorsal plates slightly longer than ventral processes, strongly narrowed near base, approaching each other, apex acute and directed ventrally; apical parts of laterophyses depressed and separated from each other, apex acute and not reaching middle emargination between dorsal plates.

Female
Unknown.

Differential diagnosis
It resembles S. limbatipennis, but can be distinguished by the following characters: tibiae black (orange in S. limbatipennis); aedeagus: basal piece with a large middle nodule at base of ventral side, lateroapical part of dorsal plate with a longitudinal ridge, apical parts of laterophyses narrowly separated from each other, clearly exceeding middle emargination between dorsal plates (while middle nodule small, dorsal plate not ridged at lateroapical part, apical parts of laterophyses widely separated and just reaching middle emargination in S. limbatipennis, see Yang et al. 2021: figs 3g-i); female abdominal sternite VIII: posterior margin rectangularly emarginate in middle, membrane behind the middle emargination triangularly bilobed at apex (while roundly emarginate in middle, membrane behind the middle emargination tapered at apex in S. limbatipennis, see Yang et al. 2021: fig. 8c); female reproductive system: diverticulum and spermatheca extremely long (relatively short in S. limbatipennis, see Yang et al. 2021: fig. 6c).

Male
HeAd. Subquadrate, surface densely and finely punctate, each side with a smooth and rectangular impression behind antennal socket; eyes moderately protruding, head width across eyes 1.5 times wider than pronotum; terminal maxillary palpomeres long-triangular, widest in middle; antennae filiform, roughly extending to ⅔ length of elytra, antennomeres II about 2.2 times as long as wide at apices, III about 1.6 times longer than II, IV-XI each with a smooth longitudinal impression in middle of outer edge, VII longest, XI distinctly longer than X, XI slightly thickened, pointed at apex.
pronotum. Subquadrate, about 1.1 times as long as wide, anterior margin arcuate, anterior angles subrounded, lateral margins nearly parallel and slightly sinuate, posterior margin slightly sinuate and narrowly bordered, posterior angles sub-rectangular, disc strongly convex on posterolateral parts, surface finely and densely punctate.
elytrA. Nearly parallel-sided, about 3.8 times as long as humeral width, 4.8 times longer than pronotum, surface finely and densely punctate, with hardly visible longitudinal costae.
AedeAgus (Fig. 10D-F). Moderately swollen laterally at basal part, reduced apically in diameter; basal piece nearly as long as dorsal plate of each paramere, with a large, bifurcate conjoined middle nodule at base of ventral side; ventral processes of parameres approaching each other, short and slightly thickened apically, bent ventrally in lateral view; dorsal plates slightly longer than ventral processes, abruptly narrowed near base and approaching each other, apex acute and directed ventrally, lateroapical part with a ridge; apical parts of laterophyses depressed and separated from each other, apex acute and clearly exceeding middle emargination between dorsal plates.

Female
Similar to male, but body stouter than male, eyes small, less protruding, head width across eyes 1.3 times wider than pronotum, antennae shorter and roughly extending to elytral mid-length, IV-XI without smooth longitudinal impressions; elytra about 3.4 times as long as humeral width.
AbdominAl sternite Viii (Fig. 7E). Moderately narrowed posteriorly, lateroapical angles widely rounded, posterior margin widely and rectangularly emarginate in middle and feebly sinuate on both sides, behind the notch with a membrane which is sclerotized and triangularly bilobed at apex.
internAl orgAn of reproductiVe system (Fig. 12C). Vagina elongate, with median oviduct situated at ventroapical part, vagina abruptly narrowed in apical part and extended into a short duct which diverticulum and spermathecal duct are arising from; diverticulum extremely long, about 0.99 times adult body length, evenly thinned apically, slender tube-shaped and spiral; spermathecal duct slightly long but much shorter than diverticulum; spermatheca slender tube-shaped and spiral, obviously thinner than spermathecal duct and much longer than diverticulum, with basal part extended into a short tube, at opening of accessory gland. Accessory gland thin in basal part and remainder moderately thin, obviously shorter than spermatheca.

Variation within species
Sometimes posterior margin of pronotum arcuate.

Differential diagnosis
Resembles S. jindrai (Fig. 5A), but differs in the following characters: pronotum and elytra uniformly light yellow, while pronotum dark brown, lightened at anterior angles, elytra honey yellow, sienna at humeri and outer part in S. jindrai; aedeagus: apex of dorsal plate slightly narrowed, middle emargination between dorsal plates moderately deep, nearly as long as half its length, apical parts of laterophyses reaching middle emargination between dorsal plates, while dorsal plate strongly narrowed, middle emargination much longer than half length, laterophyses clearly exceeding middle emargination in S. jindrai (Švihla 2004: figs 155-156).

Etymology
The specific name is derived from the Latin 'mimus' ('imitate'), and the name of the similar species S. jindrai.
HeAd. Subquadrate, surface sparsely and finely punctate, each side with a smooth and rectangular impression behind antennal socket; eyes strongly protruding, head width across eyes 1.5 times wider than pronotum; terminal maxillary palpomeres long-triangular, widest in middle; antennae filiform, extending ¾ of the length of elytra, antennomeres II about 1.7 times as long as wide at apices, III about 1.9 times longer than II, IV longest, XI slightly longer than X, pointed at apex.
pronotum. Subrounded, about 0.9 times as long as wide, anterior margin nearly straight, anterior angles roundly truncate, lateral margins slightly sinuate, posterior margin nearly straight and narrowly bordered, posterior angles sharp, protruding, disc distinctly convex on posterolateral parts, surface finely and densely punctate.
elytrA. Nearly parallel-sided, about 3.7 times as long as humeral width, 6.1 times as long as pronotum, surface finely and densely punctate, with hardly visible longitudinal costae.

AedeAgus (Figs 10G-I).
Weakly swollen dorsally in basal part, reduced basally in diameter; basal piece slightly shorter than dorsal plate of each paramere, with a large, bifurcate conjoined middle nodule at base of ventral side; ventral processes of parameres approaching each other, long and slightly narrowed apically, bent ventrally in lateral view; dorsal plates slightly longer than ventral processes, evenly narrowed apically, apex slightly acute and bent ventrally, outer margins of dorsal plates folded ventrally; apical parts of laterophyses depressed and next to each other in middle, apex acute, reaching middle emargination between dorsal plates.

Female
Unknown.

Stenothemus laticornis
It appears to resemble S. hajeki Švihla, 2011 (from China: N Yunnan), but differs in the following characters: apices of femora yellow, while uniformly black in S. hajeki; antennae almost reaching apices of elytra, while clearly exceeding them in S. hajeki (Švihla 2011: fig. 19); aedeagus: ventral processes of parameres strongly approaching each other, distinctly thickened apically and bent dorsally, while in S. hajeki (Švihla 2011: figs 93-95) the slightly approach each other, and are slightly thickened and bent ventrally.

Etymology
The specific name is derived from the Latin 'latus' ('wide') and 'cornus' ('horn'), referring to its flattened and widened antennae.

Male
HeAd. Subquadrate, surface densely and finely punctate, each side with a smooth and rectangular impression behind antennal socket; eyes strongly protruding, head width across eyes 1.5 times wider than pronotum; terminal maxillary palpomeres long-triangular, widest at basal ⅔; antennae filiform, almost reaching apices of elytra, antennomeres II about 1.1 times as long as wide at apices, III about 2.9 times longer than II, IV-XI flattened and each with a small and smooth oval impression in middle of outer edge, IV widest, V to XI gradually narrowing towards apex, XI slightly longer than X, pointed at apex.  pronotum. Subquadrate, about 1.1 times as long as wide, anterior margin arcuate, anterior angles obtuse, subrounded, lateral margins slightly sinuate, posterior margin slightly sinuate and narrowly bordered, posterior angles sub-rectangular, disc strongly convex on posterolateral parts, surface finely and densely punctate.
elytrA. Nearly parallel-sided, about 3.6 times as long as humeral width, 4.6 times as long as than pronotum, surface finely and densely punctate, with hardly visible longitudinal costae.
AedeAgus (Fig. 11A-C). Moderately swollen laterally at basal part, strongly reduced in diameter apically; basal piece nearly as long as dorsal plate of each paramere, with a large, bifurcate conjoined middle nodule at base of ventral side; ventral processes of parameres strongly approaching each other, short and distinctly thickened apically, bent dorsally in lateral view; dorsal plates slightly longer than ventral processes, strongly narrowed near base, approaching each other, apex acute; apical parts of laterophyses depressed and separated from each other, apex wide-triangular and weakly exceeding middle emargination between dorsal plates.

Female
Similar to male, but body stouter than male, eyes small, less protruding, head width across eyes 1.4 times wider than pronotum, antennae shorter and roughly extending to elytral mid-length, IV-XI without impressions; elytra about 3.2 times as long as humeral width.
AbdominAl sternite Viii (Fig. 7F). Moderately narrowed posteriorly, lateroapical angles widely rounded, posterior margin widely and roundly emarginate in middle and feebly sinuate on both sides, behind the notch with a membrane which is sclerotized and triangularly bilobed at apex. internAl orgAn of reproductiVe system (Fig. 12D). Vagina stout, with median oviduct situated at ventroapical part, vagina abruptly narrowed in apical part and extended into a short duct which diverticulum and spermathecal duct are arising from; diverticulum moderately long, about 0.58 times adult body length, evenly thinned apically, slender tube-shaped and spiral; spermathecal duct moderately long but much shorter than diverticulum; spermatheca slender tube-shaped and spiral, obviously thinner than spermathecal duct and nearly as long as diverticulum, with basal part extended into a short tube, at opening of accessory gland. Accessory gland thin in basal part and the remainder moderately thin, obviously shorter than spermatheca.

Note
Stenothemus kansuensis Pic, 1933 is not included in the key because the type was not located by us.

Discussion
The diagnosis of Stenothemus, including male and female characters, has been summarized in previous works (e.g., Okushima & Satô 1999;Yang et al. 2021). Based on these diagnostic characters, some species should be transferred to this genus; S. davidi (Pic, 1926) (from Malthacus Kirby, 1837), S. minutissimus (Pic, 1933) (from Micropodabrus Pic, 1920 and S. singularicollis (Pic, 1933) (from Lycocerus Gorham, 1895). These species have been quite poorly known since their original descriptions. Fortunately, their types are located in MNHN, and some additional specimens are at our disposal, allowing us to clarify their status and redescribe them or provide more morphological characters to recognize them.
Based on an examination and comparison of the types, S. dinshuiensis Švihla, 2011 syn. nov. is proposed as a junior synonym of S. davidi, and S. melleus Švihla, 2005 syn. nov. is synonymized with S. singularicollis, because insufficient differences were found to justify their separation. Stenothemus shaanxiensis Švihla, 2004 should be raised to a full species from a subspecies of S. benesi Švihla, 2004, justified by differences in external appearance and the aedeagus.
Additionally, the characters of the female genitalia are provided for some previously known species. This character is considered to be of high value in defining the subfamilies of Cantharidae by Brancucci (1980), has been used in species descriptions since Okushima (2005), and has been proved helpful in differentiating species of Stenothemus in our previous work Ge et al. 2021). Thus, it is important to illustrate this structure for as many species as possible. Based on our studies, the characters of the internal reproductive system are quite stable within one species, including the number of spermatheca, the shape and relative length of the spermathecal duct, spermatheca, diverticulum and accessory gland. Usually, one well-dissected specimen is used to illustrate the characteristics of this structure for the species, but sometimes two or more examples are dissected. The spermatheca is important to maintain the viability of the spermatozoa which it stores, so a larger number of, or larger, spermathecae suggests greater reproductive potential (Paschini & Martin 2017). Since the body length varies in the adults among the species, and the spermatheca accordingly changes in length, so the ratio between the two may reflect the reproductive ability to some extent, as discussed in this study.
Finally, on the basis of our previous work (Yang et al. 2014) and the present study, we discovered that the genus Stenothemus is much more diverse in Southwest China than in the southeastern part Yang et al. 2021). Sixteen species, including five new species, are recorded here, and some further species from Yunnan and Xizang will be added in forthcoming work. The species can be identified using the key located at the end of the Results section.