This mutilation occurred about the eighth or ninth century; and the other side of the leaf was then carved with subjects taken from the gospels. It was an unnecessary injury to destroy and plane away the first design. As the new purpose was probably to decorate the panels of some shrine or book-cover, the old carvings might have been concealed when the plaques were inlaid, in the same manner as the very curious pieces were treated, now at South Kensington, n^{os.} 253, 254, and 257. It would be a subject far too extensive to attempt to give a history of the use and purpose of diptychs in the public service of the Christian Church. Their origin is to be traced to the very earliest times; perhaps to the apostolic age. Mention is made of them in the liturgy of St. Mark. Gori (or his author) quotes also the ecclesiastical hierarchy of Dionysius the Areopagite. This is certainly not the writing of the true Dionysius, the contemporary of St. Paul. Yet, putting the pseudo-Dionysius as late as the fifth century, his evidence is valuable, and he speaks of the use of diptychs as of things long known. Numerous treaties and dissertations, even long books, have been written on the subject; and it would be idle work to repeat the names of the authors who are referred to, over and over again, by most writers on ivory carvings. In fact, the learning which some of these exhibit might much better have been shown if their subject had been the primitive history and practices of the Church. Except to state the mere fact of their use, the connection of ceremonial ecclesiastical diptychs with sculpture in ivory requires only a few remarks. The common use of such diptychs is well and shortly summed up in a dissertation printed by Gori in his Thesaurus. The summary may be given in few words, and, moreover, the dissertation itself is written in explanation of the diptych of the consul Clementinus just mentioned, which we are now fortunate enough to possess in England, in the Mayer collection at Liverpool. Inside the leaves, as has been already observed, is an inscription in Greek of the eighth century, to be read during mass, desiring the people to be devout and reverent and to pray for the persons whose names were to be recited.