Peacock's Four ages of poetry ; Shelley's Defence of poetry ; Browning's Essay on Shelley.

MLA

Peacock, Thomas Love, et al. Peacock's Four Ages of Poetry ; Shelley's Defence of Poetry ; Browning's Essay On Shelley. 8th ed. Oxford: Blackwell, 1972.

APA

Peacock, T. Love, Brett-Smith, H. F. B, Browning, R., & Shelley, P. Bysshe. (1972). Peacock's Four ages of poetry ; Shelley's Defence of poetry ; Browning's Essay on Shelley. 8th ed. Oxford: Blackwell.

Chicago

Peacock, Thomas Love, H. F. B Brett-Smith, Robert Browning, and Percy Bysshe Shelley. Peacock's Four Ages of Poetry ; Shelley's Defence of Poetry ; Browning's Essay On Shelley. 8th ed. Oxford: Blackwell, 1972.