This is one of the smallest sea turtles in the world and is a very delicate, pretty little turtle. These guys have perfectly rounded shells almost like a big O which are broader than what you'd see on a green turtle for example. You'll also note the "O" is bisected by a little raised ridge from nost to tail.
At the opposite end of the scale is the loggerhead....
These get very big and are rather less pretty. You can also see on this view that the shell is much less rounded and almost triangular or diamond like in shape. Of course the other dead giveaway on a loggerhead is the, erm, "loggerhead":
It's huge. If you're wondering about why these guys are in concrete pools they were apparently being held temporarily for rehab purposes at the Haaraduwa turtle farm in Sri Lanka.