MLA

McAlmon, Robert, 1896-1956. Pound, Ezra. Box 2, folder 64-66. circa 1925-59, undated. https://collections.library.yale.edu/catalog/17202524.

APA, 6th edition

McAlmon, Robert, 1896-1956. (["Box 2, folder 64-66"])(circa 1925-59, undated)[Pound, Ezra]. https://collections.library.yale.edu/catalog/17202524.