MLA

Wescott, Glenway, 1901-1987. Kirstein, Lincoln. Box 61, folder 886. 1934-87, n.d.. https://collections.library.yale.edu/catalog/2031675.

APA, 6th edition

Wescott, Glenway, 1901-1987. (["Box 61, folder 886"])(1934-87, n.d.)[Kirstein, Lincoln]. https://collections.library.yale.edu/catalog/2031675.