Agonist is the muscle that is performing the movement, the antagonist is the opposing muscle. So in this case the biceps and triceps respectively. What you think are agonists are synergist muscles.
Bam! I knew I was off when I started typing. I was getting ready to go to boxing and didn't have time to go through my text book which is why I put the disclaimer. It would have taken me a while to find because I'm deep into the cardiorespiratory system right now and all that stuff is in the muscle development/body movement portion. Dealt_with just dealt with my bull crap and corrected it. Thanks a ton man.