linux calibre to pull kindle books off nexus7?

Hi, all. I've got the latest Calibre installed on Ubuntu 11.04, and a Nexus7 (unrooted, with the original OS on it). On the Nexus, I've got the Kindle App & have downloaded the few books I've gotten thru Kindle.

Is there a way to get my Calibre install to find them on the Nexus7? I have been successful at getting my Calibre install to connect to the Nexus7 and deal with epub books, but the Kindle books seem a little more elusive. Obviously I'd like to import them to my library. I do not have a Kindle device.

Any help or pointers (I did try searching the forum, but didn't find anything that pertained to this, tho my apologies if I did miss something) appreciated!

Thanks,
--Cindy