The previously unknown sexes of 13 species of Linyphiidae and Theridiidae are described and illustrated for the first time. These include the following members of the Linyphiidae: Centromerus furcatus (Emerton) female, Cheniseo sphagnicultor Bishop & Crosby female, Coloncus siou Chamberlin male, Dismodicus alticeps Chamberlin & Ivie female, Floricomus praedesignatus (Bishop & Crosby) female, Glyphesis idahoanus (Chamberlin) male, Gnathonaroides pedalis (Emerton) female, Lepthyphantes intricatus (Emerton) female, Scyletria inflata Bishop & Crosby female, Sisicus penifusifer Bishop & Crosby female, Walckenaeria clavipalpis Millidge male; and two members of the Theridiidae: Thymoites minnesota Levi female and Robertus crosbyi (Kaston) male. Synonymy, new records, and comments on distribution, habitat and taxonomy are also given. The generic placement of Glyphesis idahoanus (Chamberlin) and Glyphesis scopulifer (Emerton) is confirmed.