MLA

Pound, Ezra, 1885-1972. Whitehead, Alfred North. Box 55, folder 2507. 1928. https://collections.library.yale.edu/catalog/17122649.

APA, 6th edition

Pound, Ezra, 1885-1972. (["Box 55, folder 2507"])(1928)[Whitehead, Alfred North]. https://collections.library.yale.edu/catalog/17122649.