Those aren't drives - they're folders. Notice the icon.
This can sometime happen if you're using an application that's accessed a file on a mounted volume, and you eject the volume. OS X should object, but sometimes it doesn't. Since the application is expecting a file somewhere in /Volumes/External Disk/... it may create a folder under Volumes with the same name as the original mounted volume. Next time you mount the volume, it'll find that e.g. in your case, RENE MARTIN is present, so it'll mount as RENE MARTIN 1.
Generally, it's safe enough to delete them, although if the offending app is still running, it may recreate the folder.