the gymno-geo's are generally smaller, southern relatives of the more commonly kept geo's
There was a very good article on them in TFH a few years back:
http://www.tfhmagazine.com/details/arti ... -south.htm
I think the G. sp "el norte" we are getting this week are similar to the "Gymnogeophagus sp. aff. meridionalis" referenced in the article, but I could be wrong.