Have you ever seen a spider with a shell?

[Silentrunning]

Here is a spider that is quite prevalent in the North Carolina woods.

 

[Marck]

This thread has some beautiful spider pics, ...and a lot of pointless arachnophobia. I don't know what the OP mistook for a shell, but either an eggcase or ornamentation on the abdomen would both make sense. Another possibility is that part of the exoskeleton from the spider's previous instar did not fully detach.