Decorated Arch and Piscina
A piscina or sacrarium is a shallow basin placed near the altar of a church, used for washing the communion vessels. They are often made of stone and fitted with a drain, and are in some cases used to dispose of materials used in the sacraments. They are found in Roman Catholic, Anglican, and Lutheran churches, and a similar vessel is used in Eastern Orthodox churches.
Rev. C. Arthur Lane Illustrated Notes on English Church History (London: Society for Promoting Christian Knowledge, 1901)
Courtesy the private collection of Roy Winkelman