To go by the descriptions in the 17th and 18th century inventories of the Dauphin’s Treasure, and judging from the volumes of the interior of its case, this vessel, which was badly damaged during the Peninsular War, would have been formed by three pieces of rock crystal, two copper gilt mounts and a silver gilt statuette. The body would have been a piece with a diminished arch profile in the form of a boat with keel and stern. It had three gadroons, probably towards the prow. The foot, to judge by the existing fragments, was smaller, with decoration restricted to branches with rows of seeds and the candeliere motif with a termination of fruit and leaves. It is described in the 1689 Versailles inventory as resting on a base in the form of a fleuron carved in a single piece with the stem. At the stern is a crystal scallop shell where Neptune used to be seated on a dolphin. Also mentioned is a gold incrustation enamelled in black that supported the shell. Original state:

Although the piece was not stolen, it was already destroyed when it returned from Paris, since the Spanish Embassy in Paris testified in 1815 that there were no more than three fragments remaining. This report seems to have been mistaken, since the Governing Committee of the Museo de Ciencias Naturales confirmed in 1939 that there were a number of other fragments left. These are the ones preserved today.

Depictions of Neptune riding on dolphins or a scallop shell were common in the prints and jewellery of the 16th century. A design for a pendant in the repertory engraved in 1581 by Hans Baptist Collaert II (Antwerp 1566-c. 1620) shows the sea god surrounded by dolphins and riding on a scallop shell. Another later variant dating from 1582 shows Neptune with two Naiads on a dragon or sea monster. Two designs by the same author for ornamental bosses with, respectively, Neptune and Amphitrite seated on shells and drawn by dolphins were published in 1582. At the Museo del Prado, vessel O54 also had a sculpture of the god Neptune riding on a dolphin. This was stolen in 1918.