A cyclide is a pair of focal conics which are the envelopes of two one-parameter families of spheres, sometimes also called a cyclid. The cyclide is a quartic surface, and the lines of curvature on a cyclide are all straight lines or circular arcs. The standard tori and their inversions in an inversion sphere S centered at a point x_0 and of radius r, given by I(x_0, r) = x_0 + ((x - x_0) r^2)/( left bracketing bar x - x_0 right bracketing bar )^2,