Poseidon is probably to be understood here as the recipient of the woman's offering. Of note are the two inscriptions between them, describing each as beautiful (one in the masculine form, the other in the feminine).
von Bothmer, Dietrich and René d'Harnoncourt. 1950. Greek, Etruscan, and Roman Antiquities: An Exhibition from the Collection of Walter Cummings Baker, Esq. no. 93, p. 12, New York: Walter Cummings Baker.
Pevnick, Seth D. 2014. Poseidon and the Sea: Myth, Cult, and Daily Life no. 57, p. 143, London: Giles.