The reference is to Giovanni Antonio Canal, known as Canaletto. The apparently plural form 'Canaletti' was common from the eighteenth century onwards, and is used by Turner in the title of his oil painting Bridge of Sighs, Ducal Palace and Custom House in Venice: Canaletti painting ( Butlin and Joll, The Paintings of J.M.W.Turner, pp. 182-3, No. 349). It is the form used by Prout in 1830. It was the form used by William Beckford in 1780, and by Mrs. Piozzi in 1785. Constable, revised Links, Giovanni Antonio Canal 1697-1768, p.9, cite the use of the form 'Canaletti' in the 1730s by Count Tessin and the Président de Brosses. Cook and Wedderburn suggest that it was a plural form to include Canaletto's nephew Bellotto (1720 - 1780), and imply that it was an idiosyncrasy of Ruskin to use what they see as a plural form when referring only to one painter. It is certainly true that Bellotto found it profitable to use the name Canaletto, and the resulting confusion was such that in 1842 Kugler, ed. Eastlake, Handbook of the History of Painting, Part One, The Italian Schools, First Edition, p 420 uses the term Canaletto of Bellotto only, and refers to the uncle, now known as Canaletto, as Antonio Canale. Vertue, 1749 is quoted in Constable, revised Links, Giovanni Antonio Canal 1697-1768, p. 35 as saying that the name 'Canaletti' was 'indifferently used by both uncle and nephew'. However the early use of the form Canaletti, and its use in contexts which are quite clearly referring to one person, suggest that there is no reason to think that the '-i' ending is necessarily to be seen as a plural marker or a family name.