MLA

Leoncavallo, Ruggiero, 1858-1919. Unidentified. Box 10, folder 311. n.d.. https://collections.library.yale.edu/catalog/16666547.

APA, 6th edition

Leoncavallo, Ruggiero, 1858-1919. (["Box 10, folder 311"])(n.d.)[Unidentified]. https://collections.library.yale.edu/catalog/16666547.