(This has been discussed before; e.g. see my post
here, in another thread.)
These are previews. In the KoboTouch or KoboTouchExtended configuration settings, select the “Metadata, on device & advanced” tab, then enable displaying previews. You may need to restart Calibre or reconnect your device (or both) before this takes effect, but once it does, Calibre should display the preview books on your device, and allow you to delete them from your device.
Alternatively, the books should be stored as kepub files without a file extension, with some sort of GUID as their filename, in the
.kobo/kepub/ folder on your device's filesystem. You should be able to simply delete them from this folder. You may want to power your Kobo off and on again afterwards to force a full library rescan. This should stop the authors of these books from appearing in the Authors view of My Books, but I haven't tested it for myself.
Good luck, and happy reading.
