From what I remember there was also the Sapphire weapon which was a mandatory battle and very easy. I believe that was the one you fought in front of Midgar. I think the one shot by Junon was the sapphire weapon and the one shot by the mako cannon was the sapphire. I haven't played FF7 since maybe 2004, so I am not the best bet. But I am quite sure there was 4 weapons in FF7, Ultima, Emerald, Ruby, and Sapphire.