2. Hydnobius enomotoi sp. nov.

Japanese name: Enomoto-chadutsu-tamakinokomushi (Figs. 4–5)

Type locality. North Chishima Islands, Matua Is., inland from Dvoynaya Bay.

Type material. NORTH CHISHIMA ISLANDS: HOLOTYPE: ♂, Matua Is., inland from Dvoynaya Bay, 5.viii.1996, M. Ôhara leg. (HUMS) . PARATYPES: 1 ♀, Simushir Island, inland costal margin of Milna Cove in Kitoboynaya Bay, 10.viii.1995, M. Ôhara leg. (HUMS) ; 1 ♀, Simushir Island, inland costal margin of Malaya Bay, 18.viii.1995, M. Ôhara leg. (HUMS) ; 2 ♀♀, Ketoi Island, near Cape Storozhena, east of Kaskead water fall, 15.viii.1995, M. Ôhara leg. (HUMS) .

Diagnosis. Body 2.1–2.4 mm. Head and pronotum brown or dark brown, minutely punctate. Elytra brown, strongly punctate, and transversely strigose. Male metafemora with a small toothed spiculum.

Description. Measurements of the holotype: Body length 2.3 mm; head length 0.41 mm; head width 0.70 mm; pronotum length 0.67 mm, pronotum width 1.1 mm; elytra length 1.5 mm, elytra width 1.3 mm.

Coloration. Dorsum shining, almost unicolor or bicolored; head and pronotum brown or dark brown; elytra brown; antennomeres 1–6 brown; antennomere 9 reddish brown; remaining antennomeres dark brown; legs brown with light brown tarsi; mesoventrite and metaventrite dark brown; abdominal ventrites brown.

Body length 2.1–2.4 mm, body ca. 1.7× as long as wide, a little convex (Fig. 4B) and almost glabrous on dorsum except for very fine, short, and sparse pubescence along lateral margins and near apex of elytra.

Head about 1.6 times as wide as long, minutely punctate (Fig. 4A), ca. 0.65× as long as and ca. 0.62× as wide as pronotum; right mandible bidentate apically; left mandible with a tooth in apical third of inner margin (Fig. 4C); antennomeres 1–4 each longer than wide; antennomere 5 about as long as wide; remaining antennomeres each wider than long; antennomere 11 robust (Fig. 4D); relative lengths from antennomeres 2 to 11 as follows: 2.4: 2.5: 1.9: 1.9: 1.5: 2.5: 1.0: 2.9: 2.5: 3.1.

Pronotum ca. 1.7× as wide as long, widest ca. at basal 1/4, densely and minutely punctate (Fig. 4A), bearing a fine transverse basal groove; ca. 0.44× as long as and ca. 0.81× as wide as elytra.

Scutellum punctate as elytra.

Elytra ca. 1.1× as long as wide (Fig. 4A), widest ca. at basal 2/5 (Fig. 4A), transversely and shortly strigose, densely punctate; punctures of elytra larger than those on head and pronotum (Fig. 4A); sutural stria distinct, arising from apex to ca. apical half of elytral length.

Metathoracic wings fully developed.

Mesoventrite strongly microreticulate, impunctate, and almost glabrous except for the sparsely pubescent area between both mesocoxae; metaventrite minutely pubescent and moderately microreticulate except for smooth central part; setiferous punctures of metaventrite minute.

Legs showing distinct sexual dimorphism on metafemora as in other species of Hydnobius; metatibiae almost straight, with short and robust spines along lateral and distal margins (Figs. 4E, 4F).

Male. Metafemur ca. 2.5× times as long as wide (excluding length of projection), weakly crenulate in ca. basal 2/3 of posterior margin, with a small toothed projection at ca. apical 1/4 of posterior margin; toothed projection apically rounded (Fig. 4E).

Aedeagus robust; median lobe triangular apically in dorsal view (Fig. 5A), slender and pointed apically in lateral view (Fig. 5B). Each paramere simply straight ca. in apical 3/5, rounded apically in dorsal view (Fig. 5A), feebly dorsally expanded between apical 3/5 and 1/5, and apically rounded in lateral view (Fig. 5B); apex bearing two setae.

Female. Metafemora about 2.9 times as long as wide; abdominal sternite 8 bearing a thin spiculum ventrale at midwidth of anterior margin (Fig. 5C); coxites and stylus as shown in Fig. 5D.

Differential diagnosis. The new species resembles Hydnobius punctulatus Hampe, 1861 (Europe, Russia incl. Far East) in having the male metafemora with small toothed projections. Hydnobius enomotoi sp. nov. may be distinguished from H. punctulatus by having the parameres almost straight to about the apical 3/ 5 in dorsal view (Fig. 5A). In contrast, H. punctulatus has distinctly sinuate parameres. Hydnobius enomotoi sp. nov. is also similar to H. tibialis Sahlberg, 1903 in dorsal appearance, but can be separated from it by having relatively slender metafemora in both sexes and a small toothed projection on the male metafemora and median lobe of the aedeagus relatively weakly swollen laterally ca. at the apical 2/5 of the lateral margins in dorsal view (Fig. 5A) (in contrast, metafemora are robust, the femoral projection is large, and median lobe relatively strongly swollen laterally in H. tibialis).

Etymology. The specific name is dedicated to a shogun’s retainer, Takeaki Enomoto (1836– 1908), who contributed to the reclamation of Hokkaido and Chishima Islands.

Distribution. North Chishima Islands (Matua Island, Simushir Island, Ketoi Island).