[11] Euphemus birthplace is given as "the banks of the Cephissus" by Pindar[12] or Hyria in Boeotia by the Megalai Ehoiai,[13] but his later residence was Taenarum in Laconia.
When the Argonauts stop by the lake Tritonis in Libya, they encounter Eurypylus, a son of Poseidon, who offers them a clod of earth as a sign of hospitality.
Euphemus takes the clod with instructions to throw it on the ground beside the entrance to the Underworld at Taenarum by which his descendants in the fourth generation would then rule over Libya.
[3][4][18] The Argonautica by Apollonius Rhodius appears to follow a different version of the same myth: in the poem, when the Argonauts arrive near Lake Tritonis, Euphemus accepts the clod of earth from Triton who first introduces himself as Eurypylus but later reveals his true divine identity.
Euphemus consults Jason about this dream and, following his advice, throws the clod in the sea, whereupon it transforms into the island Calliste (Thera).