If you want to sort out Tityus from Centruroides, simply look at the dentition of the chela teeth. Over 12 rows = Tityus. Less than 9 = Centruroides. You don't need a microscope and a count in general, though -- it is pretty apparent since there is a fairly wide spread.
If the focus on the first picture in the last set had been different, we probably could have told. I would recommend getting a lot of light (take the pics outdoors in the sunshine -- that will give you plenty) and trying again. The key is going to be getting the "pincers" in focus -- if you can get them in focus and open that is even better.
Tityus aren't really "supposed" to be in Mexico -- but I have no problem imagining some species turning up on the Gulf coast.
Cheers,
Dave
P.S. When it comes to scorpion deaths in Mexico, the yellow stripey guys are usually the ones responsible, not C.gracilis. That being said, if there is a population of Tityus, some of those can be quite nasty.
