MLA

Koch, Frederick R. (Frederick Robinson). Other correspondents. Box 49, folder 1026. [1880]-[1920], n.d.. https://collections.library.yale.edu/catalog/16600551.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 49, folder 1026"])([1880]-[1920], n.d.)[Other correspondents]. https://collections.library.yale.edu/catalog/16600551.