MLA

Cullen, Countee, 1903-1946. Thomas, Rughmarie. Box 2, folder 24. 1925-26. https://collections.library.yale.edu/catalog/16731070.

APA, 6th edition

Cullen, Countee, 1903-1946. (["Box 2, folder 24"])(1925-26)[Thomas, Rughmarie]. https://collections.library.yale.edu/catalog/16731070.