MLA

Koch, Frederick R. (Frederick Robinson). Cossmann, Bernhard. Box 59, folder 1337. n.d.. https://collections.library.yale.edu/catalog/16601869.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 59, folder 1337"])(n.d.)[Cossmann, Bernhard]. https://collections.library.yale.edu/catalog/16601869.