D. MACLISE R.A. DES. / L.C. WYON FEC.
BHM#2416 55mm AV, RRR. AE N.
The scant descriptions of this medal only mention the scenic elements from his art portrayed on the reverse, the presence & hence the significance of the Dioscuri(Castor & Pollux), Cassiopeia & the Three Graces is not mentioned, except it is suggested the 3 females represent the 3 primary colours or the colours of the rainbow.
The Dioscuri(Greek) can be recognized by the skull-cap they wear, the pilos, which was explained in antiquity as the remnants of the egg. Whether the children are thus mortal or half-immortal is not consistent among accounts, nor is whether the twins hatched together from one egg. In some accounts, only Pollux was fathered by Zeus, while Leda and her husband Tyndareus conceived Castor. This explains why they were granted alternating immortality. One would live among the gods, whilst the other was among the dead and visa versa. They are also known as the Gemini or Castores in Latin. Skilled in taming wild horses and often depicted standing by them holding the reins.
Cassiopeia is a W shaped constellation it rotates around the celestial pole and is up-side down half the time. The five brightest stars of Cassiopeia - Alpha, Beta, Gamma, Delta, and Epsilon Cassiopeiae - form the characteristic W-shape all five are prominent naked eye stars. They are oriented as a W when below Polaris during northern spring and summer nights. In northern winter they are above Polaris and the W appears inverted.
The Three Graces in Greek mythology, are referred to as the Charites, they were a trio of minor goddesses named Aglaea, Thalia and Euphrosyne. These three sisters were the daughters of Zeus and the Oceanid Eurynome. The role of the Graces in Greek mythology was to spread goodwill, pleasure and mirth, and were therefore welcome guests at festivities, especially at the banquets of the gods.
Bearing in mind that this is a memorial medal issued after his death, it appears to me that the Dioscuri's inclusion is meant to represent the circle of life, days, seasons, years & death, the sun still rises, Cassiopeia still rotates in the heavens and life on Earth goes on and though Turner the man is dead, his art has placed Turner among the immortals and the 3 Graces await to welcome him to the banquet of the Gods.