MLA

Portsmouth Theatre (Portsmouth, England). At the new theatre in Portsmouth, on Friday evening, September 18th, will be presented a tragedy, call'd Tancred and Sigismunda ... : to which will be added a farce, call'd The author ... tickets to be had at the Fountain ... and at Mrs. Lee's lodgings, at Mr. Gray's, opposite the theatre. [1761]. https://collections.library.yale.edu/catalog/33208738.

APA, 6th edition

Portsmouth Theatre (Portsmouth, England). ([1761])[At the new theatre in Portsmouth, on Friday evening, September 18th, will be presented a tragedy, call'd Tancred and Sigismunda ... : to which will be added a farce, call'd The author ... tickets to be had at the Fountain ... and at Mrs. Lee's lodgings, at Mr. Gray's, opposite the theatre]. https://collections.library.yale.edu/catalog/33208738.