MLA

Dreier, Katherine S. (Katherine Sophie), 1877-1952. Matta Echaurren, Roberto Sebastián. Box 23, folder 682. 1941-49, n.d.. https://collections.library.yale.edu/catalog/2008718.

APA, 6th edition

Dreier, Katherine S. (Katherine Sophie), 1877-1952. (["Box 23, folder 682"])(1941-49, n.d.)[Matta Echaurren, Roberto Sebastián]. https://collections.library.yale.edu/catalog/2008718.