Amphilophus labiatus, or red devil had a longer slimmer body with a pointy snout.
Amphilophus citrinellus, or the midas cichlid is deep bodied with a rounded snout and develops quite a nuchual hump as adults. both come in many colors; red, orange, white, striped, and other combinations.
here is a pic of a female yellow midas i had a while back.
and here is a pic of my red devil.
the best way to tell them apart is to look down at the fish from above if the lips are rounded it is a midas, if they are pointy it is a red devil. to compound this matter a lot of the fish being sold as 'red devils' may be Amphilophus labiatus, Amphilophus citrinellus, or a cross breed of the 2.
here is a picture of a labiatus/citrinellus cross that i currently own.
also here is a very good article on the red devil complex.
http://www.cichlidae.com/articles/a106.html