The reference is to Notebook M2 p.95, where it is called the 23rd capital of the Ducal Palace Series of Capitals of Lower Arcade. This is numbered from the Molo/Piazzetta corner capital, a system which Ruskin abandoned; hence, presumably, the number he wrote above using his final system for the Ducal Palace series of capitals of Lower Arcade. In the final system it is the 23rd Capital of the Ducal Palace Lower Arcade.
[Version 0.05: May 2008]