I read it as:
- Every galley needs to transport one element;
- For the first four galleys, these can be Sp(O) hoplites, Pk(F) Iphikrateans (if at the right dates), Ps(O) archers, or Ps(I);
- But since the Ps(I) rowers can only be used for galleys after the fourth, if you use Ps(I) in triremes 1-4 they must come from the javelinmen allowance;
- Galleys 5-6 can take any of the above, or can take Ps(I) from the rowers allowance.
I can't remember what the reasoning behind this was, if indeed there was any.