Key to species of Hydnobius in Japan and North Chishima Islands

1. Body length 2.5–3.0 mm, body ca. 1.9× as long as wide (Fig. 2A); male metafemora bearing a large toothed projection (Fig. 2E); female abdominal sternite 8 bearing a robust spiculum ventrale at anterior margin (Fig. 3C). ................................................................. ........................................................................ 1. H. akitsuensis Hoshina & Sunada, 2003

– Body length 2.1–2.4 mm, body ca. 1.7× as long as wide (Fig. 4A); male metafemora bearing a small toothed projection (Fig. 4E); female abdominal sternite 8 with a thin spiculum ventrale at anterior margin (Fig. 5C). ........................................... 2. H. enomotoi sp. nov.