"Bel Esprit"
MLA
Bird, William, 1888-1963. "Bel Esprit". Box 2, folder 64. n.d.. https://collections.library.yale.edu/catalog/16164954.
APA, 6th edition
Bird, William, 1888-1963. (["Box 2, folder 64"])(n.d.)["Bel Esprit"]. https://collections.library.yale.edu/catalog/16164954.