MLA

Koch, Frederick R. (Frederick Robinson). Magrini, Angelo (from other correspondents). Box 49, folder 1043. 1916-24, n.d.. https://collections.library.yale.edu/catalog/16064684.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 49, folder 1043"])(1916-24, n.d.)[Magrini, Angelo (from other correspondents)]. https://collections.library.yale.edu/catalog/16064684.