Antonio González Velázquez, Sacra Conversazione
Oil on canvas
The six saints are identified as follows:
On the far left, St. Peter of Alcántara holds the pen and book representing his Treatise on Prayer and Meditation. The dove of the Holy Spirit whispers in his ear, a detail common in images of St. Gregory the Great but rare in those of this saint.
Standing at Peter's proper left is an abbess holding a crozier. The source identifies her as "St. Gertrude the Great" – i.e. Gertrude of Helfta – but that Gertrude was not an abbess. She is being confused with Gertrude of Hackenborn, abbess of the Helfta monastery.
Standing behind Gertrude is St. Anthony of Padua. His attribute is the lily stalk in his right hand. He can also be recognized by the look he exchanges with the Christ Child, who is often pictured with him.
On the right side, holding the skull and gazing on the Virgin Mary, is St. Francis of Assisi.
At Francis's left shoulder St. John Nepomuk holds a crucifix, his attribute. His other hand holds a palm branch signifying his martyrdom.
Standing behind John Nepomuk, St. Philip Neri wears a chasuble and holds another lily stalk. At his neck is the collar characteristic of his order.
Mary wears the customary red robe and blue mantle. The circle of stars behind her head is borrowed from images of the Immaculate Conception. The device of showing the child naked but for a bit of cloth or some such thing goes back to the 16th century.
Source: this page at Wikimedia Commons.