Bohemian dome

A circle slides with its centre on a second circle, its plane kept parallel to one fixed plane, and sweeps out this quartic surface. It is a torus that passes through itself. The crossing is a piece of a hyperbola, and it straightens into two segments when the two circles are equal.

(a cos u, b cos v + a sin u, c sin v)

On mathcurve.com as Dôme de Bohème