I think it's Vespasian, he had his 6th Consul in 75 AD, Titus had his 6th in 77 AD when Vespasian was still Emperor (69 - 79), also Titus's bust wasn't quite so ugly. However after saying all that the inscription COULD read, starting at 5 o'clock going anti clockwise, T CAESAR IMP VESPASIANUS, which would make it Titus, but the T CAE bit is very worn and I can't make it out very well.