It wasn't one that I'm familiar with. To be honest, I'm not entirely certain it was a hellhound; that's simply the easiest and best way I knew to describe it. I've done a fair amount of research on it this evening, and I believe that this was the closest I coukd come to finding both a photograph and description of it. Therefore it must have been a Hound of Tindalos, but I'm afraid I am entirely unfamiliar with that mytbology.