Greg is correct about that. Most of the state of Florida is all pictiventris, but they can be extremely variable on their pattern, coloration, and bellies, even in the same pond..LOL!
I think this link will help clear some things up for you, as well as many others. The illustration along with the helpful captioning below it really help.
cheers, ~Doug
Range of banded Nerodia
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"a snake in the grass is a GOOD thing" 

serpentinespecialties.webs.com

