Although Cook and Wedderburn describe no. 49 in the Reference Series as filled by a Fairfax Murray drawing after Tintoretto (catalogued here as no. 49bis), the passage from Ruskin's catalogue which they reproduce in their main text lists the frame as blank (to be filled with work by Tintoretto, 'not yet chosen').
Ruskin, John, Catalogue of Examples Arranged for Elementary Study in the University Galleries (Oxford: Clarendon Press, 1870), cat. Standard no. 49
Ruskin, John, Catalogue of the Reference Series Including Temporarily the First Section of the Standard Series (London: Smith, Elder, [1872]), cat. Standard no. 49
Ruskin, John, ‘The Ruskin Art Collection at Oxford: Catalogues, Notes and Instructions’, Edward T. Cook and Alexander Wedderburn, eds, The Works of John Ruskin: Library Edition, 39 (London: George Allen, 1903-1912), 21, cat. Standard no. 49