MLA

H. D. (Hilda Doolittle), 1886-1961. Sinclair, May; Singleton, Elizabeth. Box 16, folder 535. 1925-26, 1961. https://collections.library.yale.edu/catalog/17064199.

APA, 6th edition

H. D. (Hilda Doolittle), 1886-1961. (["Box 16, folder 535"])(1925-26, 1961)[Sinclair, May; Singleton, Elizabeth]. https://collections.library.yale.edu/catalog/17064199.