Oncus

(Ὄγκος), a son of Apollo, and founder of Onceium in Arcadia. Demeter, after being me tamorphosed ilto a horse, mixed among his herds, and gave him the horse Arion, of which she was the mother by Poseidon. (Paus. 8.25.4, &c.; comp. Step. Byz. s. v.) [L.S]