Lituus

Roger Cotes named it in 1722 after the lituus, the crook-topped staff of the Roman augurs. Its angle varies inversely with the square of the radius, so it winds in toward the centre while its outer arm straightens toward the x axis. Each circle about the centre cuts from it a sector of the same area, shaded in the drawing.

r = a/√θ

On mathcurve.com as Lituus