Apparently it was around 1 metre long and heavily armoured by a shell that acted like a cage containing the internal organs. The carapace and plastron were already in the modern form but it had also some additional plates along the shell that, probably, protected its legs. Its tail was protected by spikes and ended in a sort of club.
It could not retract its neck, which was, again, protected by small spines. Overall, not a very pretty site. But again, who needs pretty when you are the oldest bag in the turtledom? For a few years "Proga" was sitting quite happily on a shelf in the American Museum of Natural History and it was showing off its fossilised remains. It must have been a very popular turtle because it had many nicknames: Chelytherium ("Turtle Beast"), Psammochelys ("Sand Turtle"), Stegochelys ("Roof Turtle") and Triassochelys ("Triassic Turtle"), like an Apollo Creed from the Triassic time. A big boost to one's ego, I'd say.
Thanks for your attention and see you in a while with a real funny bunch from the Jurassic period.