MLA

Pound, Ezra, 1885-1972. American Imperialist: typescript. Box 126, folder 5221. n.y. [Mar 14?]. https://collections.library.yale.edu/catalog/17122831.

APA, 6th edition

Pound, Ezra, 1885-1972. (["Box 126, folder 5221"])(n.y. [Mar 14?])[American Imperialist: typescript]. https://collections.library.yale.edu/catalog/17122831.