d3.svg.area.radial = function() {
  var area = d3_svg_area(d3_svg_lineRadial);
  area.radius = area.x, delete area.x;
  area.innerRadius = area.x0, delete area.x0;
  area.outerRadius = area.x1, delete area.x1;
  area.angle = area.y, delete area.y;
  area.startAngle = area.y0, delete area.y0;
  area.endAngle = area.y1, delete area.y1;
  return area;
};