MLA

Koch, Frederick R. (Frederick Robinson). Seligman, Sybil. Box 50, folder 1055. 1908-09. https://collections.library.yale.edu/catalog/16101628.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 50, folder 1055"])(1908-09)[Seligman, Sybil]. https://collections.library.yale.edu/catalog/16101628.