This is the fourth manga arc that generally goes along with the fourth (and final english) season of the anime. The "Dream" arc is where we meet Queen Nehelenia, the Dead Moon Circus, Helios, and the Amazoness Quartet. This is also where we see the Golden Crystal and see the magical Golden Kingdom and it's ruler.
There are 11 acts in this arc.
The acts:
Act 39: Dream 1, Eclipse Dream
Act 40: Dream 2, Mercury Dream
Act 41: Dream 3, Mars Dream
Act 42: Dream 4, Jupiter Dream
Act 43: Dream 5, Venus Dream
Act 44: Dream 6, New Soldiers Dream
Act 45: Dream 7, Mirror Dream
Act 46: Dream 8, Elysion Dream
Act 47: Dream 9, Dead Moon Dream
Act 48: Dream 10, Princess Dream
Act 49: Dream 11, Earth and Moon Dream
~Sailor Cosmos