Third-order space curves (cubic space curves) can be divided into four types depending on how they intersect the distance plane. The plaster models of Series VI, No. 6 from Martin Schilling's catalog (1911) show the four types on second-order cylinders (square cylinders).

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Model 6a bears the cubic ellipse on an elliptical cylinder. The cubic ellipse intersects the distance plane at one real and two imaginary points. The curve has a generatrix of the cylinder as an asymptote, which, however, is not highlighted in the model.