MLA

Koch, Frederick R. (Frederick Robinson). Duplay, Maurice. Box 48, folder 994. [1910 ca. Sep 8]. https://collections.library.yale.edu/catalog/16601855.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 48, folder 994"])([1910 ca. Sep 8])[Duplay, Maurice]. https://collections.library.yale.edu/catalog/16601855.