This .NET class wraps the AcGeEllipArc3d ObjectARX class. It represents both full ellipses and elliptical arcs in 3D space.

Autodesk.AutoCAD.Geometry.Entity3d
    Autodesk.AutoCAD.Geometry.Curve3d
        Autodesk.AutoCAD.Geometry.EllipticalArc3d

Public sealed Class EllipticalArc3d
Inherits Curve3d

public sealed class EllipticalArc3d : Curve3d;