(Figs 2, 8, 14, 20, 32–35)

Type locality. Yemen, Socotra Archipelago, Socotra Island,Noged plain,Qaareh,ca.12°20ʹ10ʺN, 53°37ʹ56ʺE, 57 m a.s.l.

Type material examined. HOLOTYPE: J (NMPC): Yemen, Socotra Is., QAAREH (waterfall), Noged plain, 5.-6. xii.2003, N 12°20ʹ10ʺ E 53°37ʹ56ʺ, 57 m [GPS], leg. P. Kabátek // YEMEN – SOQOTRA, 2003, Expedition; Jan Farkač, Petr Kabátek & David Král.

Description. Body length 11.5 mm. Body width 5.8 mm. Black, dull, glabrous. Body elongate, oval (Fig. 2).

Figs 28–61. 28, 32, 36, 40, 44, 48 – tegmen in ventral view. 29, 33, 37, 41, 45, 49 – median lobe in ventral view. 30, 34, 38, 42, 46, 50 – tegmen in lateral view. 31, 35, 39, 43, 47, 51 – median lobe in lateral view. 52, 54, 56, 58, 60 – ovipositor in ventral view. 53, 55, 57, 59, 61 – ovipositor in dorsal view. 28–31, 52–53 – Histeromorphus carinatus sp. nov.; 32–35– H. convexicostatus sp. nov.; 36–39, 54–55– H.nogedensis sp. nov.; 40–43, 56–57 – H. plicatipennis Waterhouse, 1881; 44–47, 58–59 – H. plicatus Kraatz, 1865; 48–51, 60–61 – H. undatus Gahan, 1900.

Head very sparsely and finely punctate anteriorly (Fig. 8). Anterior margin of clypeus strongly sinuate and therefore bidentate. Clypeus sparsely and roughly punctate, frontoclypeal suture slightly indicated laterally.

Pronotum smooth, glabrous, broadest in anterior third. Sides of pronotum rounded in anterior third and then straight and slightly narrowing towards pronotal base. Anterior corners acute-angled. Posterior corners obtuse-angled. Posterior half of pronotum with two shallow but distinct rounded impressions.

Elytra broad, elongate, with slightly rounded nearly subparallel sides. Each elytron with six strongly convex elytral interstriae. Space between elytral suture and first elytral striae slightly convex. Pseudopleura completely separated from elytra by complete and strongly developed, almost costate pseudopleural margin (Fig. 20); the latter starting from humeral angles and running obliquely downwards towards elytral apex below rounded edge of elytra (when viewed from behind).

Ventral part. Prosternum glabrous, smooth, impunctate. Prosternal apophysis as broad as procoxae, widened behind coxae. Mesoventrite glabrous, smooth, longer (in ventral view) than coxae. Metaventrite glabrous, smooth, as long (in ventral view) as coxae. Abdominal ventrites glabrous, smooth. Meso- and metaventrite with abdominal ventrites I and II gibbous.

Legs. Profemur distinctly claviform (Fig. 14), its dorsal side sparsely covered with short erect yellowish setae.

Male genitalia. Aedeagus simple (Figs 32–35). Apical piece of tegmen narrowed at its base, gradually narrowing towards apex then rapidly narrowing at apex, with short opening on its ventral side; base of apical piece straight and with distinct teeth. Basal piece subparallel. Median lobe almost straight in lateral view.

Female. Unknown.

Differential diagnosis. Histeromorphus convexicostatus sp. nov. differs from the remaining species of the genus mainly in having straight and strongly convex elytral interstriae, a distinct aedeagal shape (Figs 32–35), and a complete and strongly developed, nearly costate, pseudopleural margin of elytra. It shares the latter character with H. undatus but it has a strongly sinuate anterior margin of clypeus (straight in H. undatus), the pronotum is broadest in anterior third (broadest at elytral base in H. undatus), and the elytral surface is different (H. undatus possesses conspicuous transverse wavy lines on elytra).

Etymology. Refers to strongly convex elytral intestriae; adjective.

Distribution. So far known only from a single specimen collected in western Noged plain, south coast of Socotra Island.