That's the trickiest part of this -- I don't have direct access to payroll / hard evidence. It doesn't look like a negotiation gap, unfortunately -- it looks like it's more on the company's end. I have enough equity that I want the company to succeed -- I also know we're losing top women because of it.
I think ultimately than it would be best to move on, tell the cofounders what you suspect is happening and let them know they are losing top talent because of it. Its really unfortunate that you have to do that in 2014, but it might be the first time that you encounter illegal things being done to the detriment of employees or customers but it won't be the last. The best thing to do for you is to leave, and not worry about. The last you want is for them to tell their network that you are slandering them or you are a "bad employee". Its unfortunate that they are probably the kind of people that would also try to ruin your career. It sucks, but there isn't much you can do/should do without hard evidence.