Genus Hydrophilus Geoffroy, 1762

(Figs. 2C, 56–59, 64C, 66D)

Diagnosis. Larvae of this genus are easily distinguishable from other Japanese genera of the Hydrophilini by their large body size; additional diagnostic characters are: (1) frontal lines U-shaped, forming a straight line in posterior part of the head (Fig. 58A); (2) nasale smooth (Fig. 56C); (3) epistomal lobes almost symmetrical, rounded (Fig. 56C); (4) mandibles asymmetrical, right mandible with two inner teeth, left mandible with one inner tooth (Figs. 57 B–C); (5) abdominal segments with short setiferous projections on each side.