MLA

Leoncavallo, Ruggiero, 1858-1919. Unidentified. Box 10, folder 309. 1902 Dec 12. https://collections.library.yale.edu/catalog/16666545.

APA, 6th edition

Leoncavallo, Ruggiero, 1858-1919. (["Box 10, folder 309"])(1902 Dec 12)[Unidentified]. https://collections.library.yale.edu/catalog/16666545.