HALIRRHOTHIUS

a son of Poseidon and Euryte. He attempted by violence to seduce Alcippe, the daughter of Ares and Agraulos, but he was taken by surprise by Ares, who killed him. (Apollodorus iii.)

From Hesiod, Homeric Hymns, and Homerica Fragment #62:
-- Scholiast on Pindar, Ol. x. 83:
Some write `Serus the son of Halirrhothius', whom Hesiod mentions: `He (begot) Serus and Alazygus, goodly sons.' And Serus was the son of Halirrhothius Perieres' son, and of Alcyone.