While not based on morphology, the Jeweled Tailed Slug is very common in this area. P. elegans, the Elegant Tailed Slug is not. After searching for over 20 years, I recorded elegans in Athens County for the first time ever this past summer.
I prefer to look at the tails sticking out the back end. On spinuloides the tails are short. On bicaudata, (meaning two tails), the tails are twice as long as the above.
On the Early Button Slug, T. testacea, the red markings may be less wide on the sides, and the borders less even. That isn't saying much, but I have trouble telling them apart. The adults of course are easy to separate.