MLA

Pound, Ezra, 1885-1972. Vanderpyl, Fritz. Box 53, folder 2430. 1917-20. https://collections.library.yale.edu/catalog/32160352.

APA, 6th edition

Pound, Ezra, 1885-1972. (["Box 53, folder 2430"])(1917-20)[Vanderpyl, Fritz]. https://collections.library.yale.edu/catalog/32160352.