MLA

Bowen, Croswell, 1905-1971. Carmer, Carl. Box 1, folder 4. 1938-62, n.d.. https://collections.library.yale.edu/catalog/17056691.

APA, 6th edition

Bowen, Croswell, 1905-1971. (["Box 1, folder 4"])(1938-62, n.d.)[Carmer, Carl]. https://collections.library.yale.edu/catalog/17056691.