on Zane Stein's site Chiron and Friends
There was also another Amycus
The story of Argonauts on Timeless Myths
"The Argonauts soon encountered the Bebryces whose king Amycus challenged one of them in boxing match to the death. Polydeuces, one of the Dioscuri, was the best boxer among the Argonauts. The contest seemed evenly matched until Polydeuces killed Amycus through a blow to the king's ear. The Bebryces set about to attack Polydeuces, but was routed by the Argonauts."