I would personally add it to triceps/biceps, since all three are smaller muscle groups. I like to give more energy to just the chest and back. Also, shoulders are worked when you work the chest (anterior delts) or the back (rear delts) so doing chest/back/shoulders in one workout can overdo the shoulders, unless you are sure to decrease the number of exercises for the shoulders.
Just make sure to leave at least one day off in between the two upper-body workouts (ie: work back/chest on Monday, and shoulders and arms not until at least Wednesday). I suggest doing the shoulders, then biceps, then triceps, as triceps are assistance muscles for the shoulders, and doing shoulders/triceps one right after the other doesn't give the triceps enough recovery.
(FYI: the singular of "calves" is "calf", just like with baby moo-cows ;-) )