American alligators have broad snouts.
American crocodiles have pointy A-shaped snouts.
If the primate you are looking at has a tail, it must be a monkey. Apes do not have tails. However, don't be fooled, this doesn't work the other way around. If the next primate you look at has no tail, this does not mean that it must be an ape. There are some monkeys that do not have tails.