This covers the Fissipedia (terrestrial forms) and Pinnipedia (marine forms).    From Wordnik.com.  [Epinions Recent Content for Home] Reference

The Fissipedia offer an instructive example, for while the Otariidae have the hind feet turned forward and can move on land somewhat like ordinary Mammals, the Phocidae cannot move their hind legs independently or turn them forward, and can only drag themselves about on land for short distances.    From Wordnik.com.  [Hormones and Heredity] Reference