What did prehistoric turtles look like?

A Prehistoric Dolphin (also known as Ichthyosaurus) looked like the pictures shown below:

http://www.healthstones.com/dinosaurdata/i/ichthyosaurus/ichthyosaurus.jpg

http://www005.upp.so-net.ne.jp/JurassicGallery/Ichthyosaurs.jpg

http://csotonyi.com/Ichthyosaurus.jpg