What is the mouth difference about alligators and crocodiles?

Alligator's have wider jaws/noses then Crocodiles and the Alligator's upper jaw overlaps the lower so on an Alligator you can't see the lower teeth when their mouths are shut, the crocodile you can see all the teeth when the mouth is shut

A good illustration: http://crocodilian.com/cnhc/cbd-faq-q1.htm