The underside with two red sealing-wax collection marks bearing the arms of a Cardinal (see the details illustrated at the end of the catalogue), and with remnants of a black enamel X20635 inventory number.
For a cistern with marine decoration of similar type but of different form, see Elena Ivanova, Il secolo d'oro della maiolica, Ceramica italiana dei secoli XV-XVI dalla raccolta del Museo Statale dell'Ermitage (Milan, 2003), p. 89, no. 62 and Julia E. Poole, Italian maiolica and incised slipware in the Fitzwilliam Museum, Cambridge (Cambridge, 1995), pp. 374-375, no. 410. Most cisterns appear to have marine decoration perhaps due to their use as receptacles for holding water.
The triton in the centre is appears to be taken from the Quos Ego engraving by Marcantonio Raimondi after Raphael, illustrated on the previous page.