aka keyhole or button hole slots. Sturmey Archer also used them sometimes. Kind of a PITA to build - probably took me 4 or 5 tries to properly lace the wheel. One other nice "feature" of this design is that drive and non-drive spokes are virtually the same (within a milimeter IRRC.)

Here's a top-tip: I used golf tees to peg the slots and keep the spokes in place while lacing the wheel.




More pics here: http://www.flickr.com/photos/3915149...57626711955076