The story of Venus' birth is described in Hesiod's 'Theogony' and in the 'Homeric Hymns'. In the centre, Venus steps from her shell on to the island of Cyprus (or Cythera). In the rim around the central group are Neptune and Amphitrite at the top and Cupid and Psyche at the bottom.
This design was probably a modello for a silver basin. Such prestigous objects were displayed on a side table to signal the wealth of the owner.