This wraps the ObjectARX AcDbSubentRef class

Autodesk.AutoCAD.DatabaseServices.GeomRef
    Autodesk.AutoCAD.DatabaseServices.SubentRef
        Autodesk.AutoCAD.DatabaseServices.EdgeRef
        Autodesk.AutoCAD.DatabaseServices.FaceRef
        Autodesk.AutoCAD.DatabaseServices.VertexRef

Public abstract Class SubentRef
Inherits GeomRef

public abstract class SubentRef : GeomRef;