The larvae of the following species of Dytiscidae are described and figured: Laccophilus maculosus (Germ.), L. biguttatus Kirby, Liodessus affinis (Say), Hydroporus notabilis Lec, Hygrotus punctilineatus (Fall), Hyg. tumidiventris (Fall), Hyg. punctatus (Say), Hyg. patruelis (Lec.), Hyg. impressopunctatus (Schall), Hyg. canadensis (Fall), Hyg. sellatus (Lec.), Laccornis conoideus (Lec.), Rhantus notatus Fab., Colymbetes sculptilis Harr., Agabus clavatus Lec., A. discolor Harris, A. bifarius (Kirby), A. ontarionis Fall, Graphoderus zonatus (Hoppe), Acilus semisulcatus Aubé, Hydaticus stagnalis (Fab.), Dytiscus sublimbatus Lec., D. dauricus Gebler, and D. fasciventris Say. All were collected at Delta, Man.