Thankyou, Jo Anne for your comment. Biscornu apparently means "many horns" - sorry I can't remember exactly where I found that definition. I found a tremendous amount of information just by googling "biscornu" but unfortunately I don't keep very good records of my travels around the web. (Not a good admission by an exlibrarian!).
One site I did bookmarkwith a list of tutorials on how to make a biscornu pincushion, among other things, was http://focusonfinishing.wordpress.com/useful-links/
They are certainly fascinating shapes. It makes me wonder how a pair of pentagons joined in a similar way would end up. Or even more than two? I wonder has anyone made one such structure. Maybe the pentagons could be a project for the future.