My RES developed this dry spot on his shell while I was out of town a few weeks ago. I left my roommates in charge, but they said nothing unusual happened. I have just been keeping an eye on it since I got back, because I don't have the funds right now to take him to a dr. The spot has not changed at all. I attached a picture, but the flash makes the spot appear a little more discolored than it is. Hopefully you get the idea and have a solution so I can stop worrying. Thanks for your help!!