Drivers for TrekStor Surftab Xiron 7.0 3G
I had the same problem!
You have to add the vendor-id to adb_usb.ini !


  echo 0x1e68 >> $HOME/.android/adb_usb.ini


source:
https://urbanjack.wordpress.com/2014/10/23/howto-use-surftab-xiron-on-mac-for-development-adb/