Church of San Salvador, Villar das Donas, Spain
The saint on the right holds a cross, an attribute of both St. Philip and St. Andrew. What is left of the faded inscription below the saint is consistent with a reading, sanctus andreas, "St. Andrew." It does not seem possible that the second word could have been philippus. However, the saint's hair is neatly combed, whereas wild hair was a feature of St. Andrew's portraits from early times through the Middle Ages.
The saint holding a pen on the left is surely the author of the now-illegible writing on the scroll in his right hand. If he is both an apostle and a New Testament author, he would have to be James, Peter, John, or Jude. (Medievals took the author of the Epistle of James to be the apostle James the Less.) Peter is not ever portrayed without a beard, James and Jude usually not. So John?
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Read more about St. Philip, St. Andrew, and St. John the Evangelist.
Photographed at the church by Richard Stracke, shared under Attribution-NonCommercial-ShareAlike license.