Can anyone identify my trilobite?

I picked this up at the gift store on one of my son's field trips years back for $1.50, had to clean the aggregate off myself.

Since it's a pretty standard trilobite shape I assume it's an early variety, but I'm curious about it. Can anyone give some idea as to its age? Maybe the Order, Family, maybe Genus?

Also there's one shot of the underside. I've left that alone on the assumption that there's no fossil on that side, but if I *should* clean aggregate off there, please let me know.