Based on ART.Ellipse but with center in the middle rather than top/left

ART.Ellipse2.js

ART.Ellipse2 = new Class({
	
	Extends: ART.Shape,
	
	initialize: function(width, height){
		this.parent();
		if (width != null && height != null) this.draw(width, height);
	},
	
	draw: function(width, height){
		var path = new ART.Path;
		var rx = width / 2, ry = height / 2;
		path.move(-rx, 0).arc(width, 0, rx, ry).arc(-width, 0, rx, ry);
		return this.parent(path);
	}

});

http://jsfiddle.net/tofu/mjvCT/