MLA

Newell, Peter, 1862-1924. McCormick, Frederick. Box 200, folder 2511. 1941. https://collections.library.yale.edu/catalog/17181130.

APA, 6th edition

Newell, Peter, 1862-1924. (["Box 200, folder 2511"])(1941)[McCormick, Frederick]. https://collections.library.yale.edu/catalog/17181130.