I cant see the bulging but agree with wilder that it will be a viral infection perhaps a cancer.
Take a look here to see if it sounds like this but usually it white not black but with the swelling never no.
http/www.articledepot.co.uk/article-29320.htm
Look under black patches it can be old age but your dosn't sound like it with the swelling also what black angel has said it says in this article in can be cancer, sorry.
http/www.fbas.co.uk/ASK3.html#widows
Should I take it out of the current 55 gallon tank to treat with melafix. I don't really have a hospital tank anymoreI've had a few widows do this at work; it has been cured with melafix, so I'm assuming it is a bacterial infection,
provided yours are not suffering from amonia burns as wilder has said.