Stubby, Black Toenail

I think i have had this condition since a baby. Two of my toenails on my left foot are black and stubby. They are deformed and not like normal toenails. I don't know if you can imagine this in your head, but it needs to be fixed and i want to know what it is. When i say stubby i mean that the nail is really thick and goes straight down the middle of my toe. The nail doesn't completely cover the toe where it normally would. Do you have any idea of what this is?