MLA

Wilder, Thornton, 1897-1975. Kelly, Gene. Box 44, folder 1166. 1953 Dec 30. https://collections.library.yale.edu/catalog/17056651.

APA, 6th edition

Wilder, Thornton, 1897-1975. (["Box 44, folder 1166"])(1953 Dec 30)[Kelly, Gene]. https://collections.library.yale.edu/catalog/17056651.