This .NET class wraps the AcGeEllipArc2d ObjectARX class. It represents both full ellipses and elliptical arcs in 2D space.

Autodesk.AutoCAD.Geometry.Entity2d
    Autodesk.AutoCAD.Geometry.Curve2d
        Autodesk.AutoCAD.Geometry.EllipticalArc2d

Public sealed Class EllipticalArc2d
Inherits Curve2d

public sealed class EllipticalArc2d : Curve2d;