MLA

Bryher, 1894-1983. "A Letter to Bryher": typescript, original and carbon. Box 93, folder 3399. 1950. https://collections.library.yale.edu/catalog/17290870.

APA, 6th edition

Bryher, 1894-1983. (["Box 93, folder 3399"])(1950)["A Letter to Bryher": typescript, original and carbon]. https://collections.library.yale.edu/catalog/17290870.