Oncius was the son of Apollo according to tradition, and reigned in Thelpusa at the place called Onceum. And the goddess Demeter got the name Erinys in this way: when she was wandering about in quest of her daughter Proserpine, Poseidon they say followed her with amatory intentions, and she changed herself into a mare and grazed with the other horses at Onceum, and Poseidon found out her metamorphosis and changed himself into a horse and so got his ends, and Demeter was furious at this outrage, but afterwards they say ceased from her anger and bathed in the river Ladon. So the goddess got two surnames, Erinys (_Fury_) from her furious anger, for the Arcadians call being angry being a Fury, and Lusia from her bathing in the Ladon. The statues in the temple are of wood, but the heads and fingers and toes are of Parian marble. The statue of Erinys has in her left hand a cist and in her right a torch, and is one conjectures about nine feet in height, while the statue of Lusia seems six feet high. Let those who think the statue is Themis, and not Demeter Lusia, know that their idea is foolish. And they say that Demeter bare a daughter to Poseidon, (whose name they will not reveal to the uninitiated), and the foal Arion, and that was why Poseidon was called Hippius there first in Arcadia. And they introduce some lines from the Iliad and Thebaid in confirmation of this: in the Iliad the lines about Arion. “Not if one were to drive from behind the godlike Arion, swift courser of Adrastus, who was of the race of the Immortals.”[32] And in the Thebaid when Adrastus fled from Thebes, “Dressed in sad-coloured clothes with Arion dark-maned courser.” They want to make the lines indicate in an ambiguous way that Poseidon was the father of Arion. But Antimachus says he was the son of earth: “Adrastus, the son of Talaus and grandson of Cretheus, was the first of the Danai who drove a pair of much praised horses, the swift Cærus and Thelpusian Arion, whom near the grove of Oncean Apollo the earth itself gave birth to, a wonder for mortals to look upon.” And though this horse sprung out of the ground it may have been of divine origin, and its mane and colour may have been dark. For there is a tradition that Hercules when he was warring with the people of Elis asked Oncus for a horse, and captured Elis riding into the battle upon Arion, and that afterwards he gave the horse to Adrastus. Antimachus also has written about Arion, “He was broken in thirdly by king Adrastus.”