MLA

Koch, Frederick R. (Frederick Robinson). Music/Sea Idyll. Box 322, folder 1746. 1899-1900. https://collections.library.yale.edu/catalog/2014974.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 322, folder 1746"])(1899-1900)[Music/Sea Idyll]. https://collections.library.yale.edu/catalog/2014974.