MLA

Pratt, Richard Henry, 1840-1924. Stereograms, miscellaneous, 6 items. Box 23a, folder 750. n.d.. https://collections.library.yale.edu/catalog/2054659.

APA, 6th edition

Pratt, Richard Henry, 1840-1924. (["Box 23a, folder 750"])(n.d.)[Stereograms, miscellaneous, 6 items]. https://collections.library.yale.edu/catalog/2054659.