The tailpiece of the frieze shows a Silenus under a tree flanked by two standing figures which, together with their accessories (the punching bag and the waterspout), form a balanced, closed composition.

The young man punching the kώρυκος, or punching bag, performs an action, customary among Greek boxers practicing for a contest: he indicates Polydeukes.

Near a fountain a young man is drinking from his kylix. Polydeukes’ counterpart in this symmetrical scene is certainly his brother Kastor with whom he so constantly appears. He has the required youthful beard and he is further characterized by the spear and chlamys, his familiar attributes on innumerable monuments. A comparison of the two figures of the heroes engraved on two different sections of the cista frieze emphasizes the correctness of this assumption, for they are identical, downy beard and all.

The most amusing figure of this trio is the Silenus who gaily imitates Polydeukes at the expense of his own fat stomach. The appearance of such a figure in the context of the Argonauts is of particular interest given the fact that Sophokles wrote a satyrplay, Amykos.