The saints depicted are (from left to right) Anthony Abbot, John the Baptist, Julian the Hospitaller, and Francis of Assisi.
"So that now I care most for Michael Angelo, Luca Signorelli, Mantegna, Giotto, Botticelli, Andrea del Sarto. Paulo Uccello, and Piero della Francesca" and he admired "Botticelli everywhere" Memorials Vol p. 26 These quotations were taken from a sketchbook filled with drawings and observations during his 1871 trip to Italy and which is now held in the Museum of New Zealand, Wellington.