2. A fabulous horse, which Poseidon begot by Demeter; for in order to escape from the pursuit of Poseidon, the goddess had metamorphosed herself into a mare, and Poseidon deceived her by assuming the figure of a horse. Demeter afterwards gave birth to the horse Arion, and a daughter whose name remained unknown to the uninitiated. (Paus. 8.25.4
According to the poet Antimachus (apud Paus. l.c.
) this horse and Caerus were the offspring of Gaea; whereas, according to other traditions, Poseidon or Zephyrus begot the horse by a Harpy. (Eustath. ad Hom. p. 1051
; Quint. Smyrn. 4.570.) Another story related, that Poseidon created Arion in his contest with Athena. (Serv. ad Virg. Georg.
1.12.) From Poseidon the horse passed through the hands of Copreus, Oncus, and Heracles, from whom it was received by Adrastus. (Paus. l.c. ;
Hesiod. Scut. Here.