surfaces from MathCurve
Astroid :           http://www.mathcurve.com/surfaces/astroidal/astroidal.shtml
Berlingot :        http://www.mathcurve.com/surfaces/berlingot/berlingot.shtml
Bohemian dome :                           http://www.mathcurve.com/surfaces/boheme/boheme.shtml
Bonnet croisé ( Cross-cap) :          http://www.mathcurve.com/surfaces/bonnetcroise/bonnetcroise.shtml
Romaine :         http://www.mathcurve.com/surfaces/romaine/romaine.shtml