MLA

Bryher, 1894-1983. Beach, Sylvia. Box 2, folder 89. 1925-35, n.d.. https://collections.library.yale.edu/catalog/2012331.

APA, 6th edition

Bryher, 1894-1983. (["Box 2, folder 89"])(1925-35, n.d.)[Beach, Sylvia]. https://collections.library.yale.edu/catalog/2012331.