MLA

H. D. (Hilda Doolittle), 1886-1961. Pearson, Norman Holmes. Box 13, folder 451-71. 1938-61, n.d.. https://collections.library.yale.edu/catalog/2068426.

APA, 6th edition

H. D. (Hilda Doolittle), 1886-1961. (["Box 13, folder 451-71"])(1938-61, n.d.)[Pearson, Norman Holmes]. https://collections.library.yale.edu/catalog/2068426.