MLA

Pound, Ezra, 1885-1972. Del Valle, Pedro Augusto. Box 12, folder 570-571. 1954-59. https://collections.library.yale.edu/catalog/17122548.

APA, 6th edition

Pound, Ezra, 1885-1972. (["Box 12, folder 570-571"])(1954-59)[Del Valle, Pedro Augusto]. https://collections.library.yale.edu/catalog/17122548.