MLA

Brooks, Cleanth, 1906-1994. Kendall, Willmoore. Box 6, folder 147-48. 1938-60, n.d.. https://collections.library.yale.edu/catalog/17103603.

APA, 6th edition

Brooks, Cleanth, 1906-1994. (["Box 6, folder 147-48"])(1938-60, n.d.)[Kendall, Willmoore]. https://collections.library.yale.edu/catalog/17103603.