Key to the Japanese species of Diaulota

1. Body usually black (reddish black in D. aokii); head oval; male heads as large as that of female; mentum as long as wide... 2

- Body color reddish brown, but some of abdominal segments black or blackish; head rectangular; male head larger than that of female; mentum strongly transverse........................................................................4

2. Tarsal formula 4-4-4; apical lobe of median lobe unilobed in lateral view......................................... 3

- Tarsal formula 4-4-5; apical lobe of median lobe bilobed in lateral view............................... D. hokkaidona

3. Body reddish black; elytra and abdomen covered with thin and short setae; distributed in central Honshû........... D. aokii

- Body almost black; elytra and abdomen covered with long setae; distributed in southern Honshû, Shikoku and Kyûshû.......................................................................................... D. decipiens sp. n.

4. Tarsal formula 4-4-4; infraorbital carina short, shorter than half of head.......................................... 5

- Tarsal formula 4-4-5; infraorbital carina long, reaching to eye........................................... D. oharai

5. Median lobe of aedeagus: apical sclerite in lateral view; suspensonia thin; distributed in Japan sea side of Honshû and Kyûshû................................................................................... D. submarina

- Median lobe of aedeagus: apex of apical sclerite rounded in lateral view; suspensonia broad; distributed in Pacific side of Honshû and Kyûshû, and northern Ryûkyû................................................................. 6

6. Median lobe of aedeagus: apex of apical lobe pointed in ventral view; apical sclerite extend toward apical margin in ventral view; distributed in southern Honshû, Kyûshû and northern Ryûkyû....................................... D. uenoi

- Median lobe of aedeagus: apex of apical lobe truncate in ventral view; apical sclerite narrow toward apical margin; distributed in central Honshû....................................................................... D. orientalis sp. n.