MLA

Pound, Ezra, 1885-1972. Sullivan, John Patrick. Box 50, folder 2250. 1959-60. https://collections.library.yale.edu/catalog/17122637.

APA, 6th edition

Pound, Ezra, 1885-1972. (["Box 50, folder 2250"])(1959-60)[Sullivan, John Patrick]. https://collections.library.yale.edu/catalog/17122637.