Here they are with their non-extended brothers, in the full set of Billy bookcase possibilities:
Thingiverse link: http://www.thingiverse.com/thing:327165
Settings: Printed on MakerBot Replicator 2 with .3mm/low settings, with models lying flat so that support is not needed.
Technical notes, dimension/OpenSCAD flavor: The new extended models were rendered with yesterdays' bookcase module, but taller:
// wide short billy with extender
//bookcase(depth=11,length=31.5,height=55.375,shelves=4);
// wide tall billy with extender
//bookcase(depth=11,length=31.5,height=93.125,shelves=7);
// thin short billy with extender
//bookcase(depth=11,length=15.75,height=55.375,shelves=4);
// thin tall billy with extender
bookcase(depth=11,length=15.75,height=93.125,shelves=7);