MLA

Trefusis, Violet, 1894-1972. Autograph letter, signed, from Dorothy Heneage, expressing sadness due to Violet's mother's approaching death. Box 7. 1947 May 24. https://collections.library.yale.edu/catalog/16538085.

APA, 6th edition

Trefusis, Violet, 1894-1972. (["Box 7"])(1947 May 24)[Autograph letter, signed, from Dorothy Heneage, expressing sadness due to Violet's mother's approaching death]. https://collections.library.yale.edu/catalog/16538085.