MLA

Pound, Ezra, 1885-1972. Stoddard, Theodore Lothrop. Box 50, folder 2230. 1939-40. https://collections.library.yale.edu/catalog/17122633.

APA, 6th edition

Pound, Ezra, 1885-1972. (["Box 50, folder 2230"])(1939-40)[Stoddard, Theodore Lothrop]. https://collections.library.yale.edu/catalog/17122633.