MLA

Koch, Frederick R. (Frederick Robinson). Music/Unidentified/Sketches, drafts, and fragments. Box 180, folder 1522. n.d.. https://collections.library.yale.edu/catalog/2014564.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 180, folder 1522"])(n.d.)[Music/Unidentified/Sketches, drafts, and fragments]. https://collections.library.yale.edu/catalog/2014564.