I've used both Google and Bing to do a (reverse) image search on this - both came up with hundreds of hits on nothing like it.
One image bore a slight resemblance but it was circular - a spiders egg sack - the shape of mine could be due to it spanning a trough (in a cactus) but it's obviously not the same species - much thinner tethers - mine is a very impressive 101/2 point harness!
I love spiders in my garden spaces - but I'd still like a closer match. Any Ideas?
Cheers.
It certainly does look like a spider's egg sack but what a beautiful and finely made one. I can't be any more sure than you but, as you say, it's very impressive.
I guess your best hope of closer identification is to watch and hope you can catch sight of whatever emerges unless, of course, it has already slipped out - or unless it is in fact something else altogether.