(Figs 6, 12, 18, 24, 48–51, 60, 61)

Histeromorphus undatus Gahan, 1900: 8 (original description); GAHAN (1903): 290 (redescription, with figure of habitus); LESNE (1915): 228 (key to species); GEBIEN (1937): 547 (catalogue); KOCH (1970): 93 (differential diagnosis); SCHAWALLER (2004): 442 (new records); LÖBL et al. (2008): 148 (catalogue).

Type locality. Yemen, Socotra Archipelago, Abd el Kuri Island.

Type material. LECTOTYPE (here designated): unsexed spec. (BMNH): SYNTYPE [round, white with blue borders, printed] // Type [round, white with red borders, printed] // Abd-el-Kuri, 22. Feb. 990, W.R.O. Grant, 99-85 [white, printed] // Histeromorphus undatus Gahan, Type [white, handwritten] // LECTOTYPE, Histeromorphus undatus Gahan, 1900, desig. L. Purchart 2014 [red, printed]. PARALECTOTYPES: 2 unsexed spec. (BMNH): SYNTYPE [round, white with blue borders, printed] // Abd-el-Kuri, 22. Feb. 99, W.R.O.Grant, 99-85 [white, printed] // Histeromorphus undatus Gahan, Co-Type [white, handwritten] // PARALECTOTYPE, Histeromorphus undatus Gahan, 1900, desig. L. Purchart 2014 [red, printed].

Additional material examined (4 spec.). YEMEN: ABD EL KURI ISLAND: Abd-el-Kuri, 22.ii.1899, 1 ♀, W.R.O. Grant leg. (MNHN); Westküste, Umgebung Basecamp, N 12°11ʹ, E 53°14ʹ, 17.–18.ii.1999, 1 J + 1 spec., H. Pohl leg. (SMNS); ii.1999, 1 spec., W. Wranik leg. (SMNS).

Redescription. Body length 11.5–12.5 mm (lectotype: 12.5 mm), body width 7.5–8.5 mm (lectotype: 8.5 mm). Black, dull, glabrous. Body broad, oval (Fig. 6).

Head sparsely and finely punctate (Fig. 12). Anterior margin of clypeus straight. Clypeus finely and sparsely punctate, frontoclypeal suture slightly indicated laterally.

Pronotum broadest at posterior corners, smooth, glabrous. Sides of pronotum rounded. Lateral margin markedly thickened and with distinct groove along its entire length. Anterior and posterior corners sharply angled.

Elytra glabrous, with broadly rounded sides. Elytral surface with conspicuous transverse wavy lines. Pseudopleura separated from elytra by complete and strongly developed, almost costate pseudopleural margin of elytra which runs parallel with edge of elytra (Fig. 24).

Ventral part. Prosternum glabrous, slightly longitudinaly wrinkled, impunctate. Prosternal apophysis as broad as procoxae, widened apically, sparsely covered with small granules. Mesoventrite glabrous, longitudinally wrinkled, covered with small granules, as long (in ventral view) as mesocoxae. Metaventrite glabrous, longitudinally wrinkled, covered with small granules, as long (in ventral view) as metacoxae. Abdominal ventrites glabrous; abdominal ventrite I longitudinally wrinkled, covered with small granules; other abdominal ventrites smooth.

Legs. Profemur distinctly claviform (Fig. 18), dorsal side sparsely covered with short erect yellowish setae.

Male genitalia. Aedeagus simple (Figs 48–51). Apical piece of tegmen subparallel, rapidly narrowing at apex, without opening on ventral side; base of apical piece bisinuate, with distinct teeth. Basal piece widened towards base. Median lobe slightly S-like in basal half, moderately curved upwards (in lateral view) in apical half.

Female genitalia. See Figs 60, 61.

Differential diagnosis. This species can be distinguished from the other species of the genus by the straight anterior margin of clypeus (sinuate in other species), distinctly acute-angled posterior corners of pronotum (obtuse-angled in other species), longitudinally wrinkled hypomeron and longitudinally wrinkled and granulate meso- and metaventrite (completely smooth in other species), by markedly thickened lateral margin of the pronotum with a groove along its entire length (not markedly thickened and without groove in other species). With H. convexicostatus sp. nov. it shares the complete and strongly developed, almost costate pseudopleural margin of elytra (incomplete in H. plicatipennis, H. nogedensis sp. nov., and H. plicatus). In H. carinatus sp. nov. the pseudopleural carina is also complete, but it is fine and runs in different direction than in H. undatus and H. convexicostatus sp. nov.

Distribution. Known only from Abd el Kuri Island.