Is that an empty exoskeleton?

It might be. It looks just like this photo :http://www.123rf.com/photo_5267979_an-intact-exoskeleton-of-a-treehopper-nymph-genus-ceresa.html

where it is called an intact exoskeleton of a Treehopper Nymph-Genus Ceresa. And that would possibly answer my next question. Is this that particular treehopper, i.e. buffalo treehopper - Ceresa alta?

It is very likely the Buffalo, they are very common and occur in all 48 lower states, in fact it is the only treehopper I have ever seen here (and yours is the right shape and color).

Perhaps there are other Ceresa genus look-alikes.