MLA

Schwartz, Delmore, 1913-1966. Berryman, John. Box 1, folder 11. 1946-1965, undated. https://collections.library.yale.edu/catalog/17155213.

APA, 6th edition

Schwartz, Delmore, 1913-1966. (["Box 1, folder 11"])(1946-1965, undated)[Berryman, John]. https://collections.library.yale.edu/catalog/17155213.