MLA

Schwartz, Delmore, 1913-1966. Lowell, Robert. Box 1, folder 69. 1945-1946. https://collections.library.yale.edu/catalog/17078925.

APA, 6th edition

Schwartz, Delmore, 1913-1966. (["Box 1, folder 69"])(1945-1946)[Lowell, Robert]. https://collections.library.yale.edu/catalog/17078925.