This .NET class wraps the AcGeLinearEnt3d ObjectARX class. This is an abstract base class for all 3D line classes.

Autodesk.AutoCAD.Geometry.Entity3d
    Autodesk.AutoCAD.Geometry.Curve3d
        Autodesk.AutoCAD.Geometry.LinearEntity3d
            Autodesk.AutoCAD.Geometry.Line3d
            Autodesk.AutoCAD.Geometry.LineSegment3d
            Autodesk.AutoCAD.Geometry.Ray3d

Public abstract Class LinearEntity3d
Inherits Curve3d

public abstract class LinearEntity3d : Curve3d;