27. Clement X (b. 1590, Pope 1670–1676). Index librorum prohibitorum Clementis X. pontificis maximi iussu editus. Rome: Ex typographia reverendae camerae apostolicae, 1670.

In later editions of the Index librorum prohibitorum, the three classes were interspersed in one alphabetical sequence, so that heretical authors, prohibited titles, and anonymous works could be more easily found in one sequence. Thus, Galileo Galilei, an author of the second class, is listed under the letter G with a cross-reference to the one work by him that was prohibited, the famous Dialogo.