This .NET class wraps the AcGePolyline2d ObjectARX class. It's represents a piecewise linear spline entity in 2D space.

Autodesk.AutoCAD.Geometry.Entity2d
    Autodesk.AutoCAD.Geometry.Curve2d
        Autodesk.AutoCAD.Geometry.SplineEntity2d
            Autodesk.AutoCAD.Geometry.PolylineCurve2d

Public sealed Class PolylineCurve2d
Inherits SplineEntity2d

public sealed class PolylineCurve2d : SplineEntity2d;