MLA

Pound, Ezra, 1885-1972. Masterman, Lucy Blanche Lyttelton. Box 33, folder 1396. 1916. https://collections.library.yale.edu/catalog/17122594.

APA, 6th edition

Pound, Ezra, 1885-1972. (["Box 33, folder 1396"])(1916)[Masterman, Lucy Blanche Lyttelton]. https://collections.library.yale.edu/catalog/17122594.