MLA

Purdy, James, 1914-2009. Pearson, Norman Holmes. Box 3, folder 91. 1960-62. https://collections.library.yale.edu/catalog/10171235.

APA, 6th edition

Purdy, James, 1914-2009. (["Box 3, folder 91"])(1960-62)[Pearson, Norman Holmes]. https://collections.library.yale.edu/catalog/10171235.