This memoir is the fourth of a series dealing with the fauna of the Trichoptera of Canada and the adjacent States. It deals with the families Hyalopsychidae, Psychomyiidae, Goeridae, Brachycentridae, Sericostomatidae, Helicopsychidae, Beraeidae, Odontoceridae, Calamoceratidae and Molannidae. These families have been arbitrarily gathered here because of their small size and in spite of the fact that they are not all taxonomically related. In the following pages, one will find familial, subfamilial, generic and specific diagnosis of all the taxa constituting these families. Dichotomic keys are included and distributional records for each species are mapped. Ecological characters are given when possible.