This .NET class wraps the AcGeSurface ObjectARX class. Surface class is an abstract base class for all other parametric surfaces.

Autodesk.AutoCAD.Geometry.Entity3d
    Autodesk.AutoCAD.Geometry.Surface
        Autodesk.AutoCAD.Geometry.Cone
        Autodesk.AutoCAD.Geometry.Cylinder
        Autodesk.AutoCAD.Geometry.ExternalBoundedSurface
        Autodesk.AutoCAD.Geometry.ExternalSurface
        Autodesk.AutoCAD.Geometry.NurbSurface
        Autodesk.AutoCAD.Geometry.OffsetSurface
        Autodesk.AutoCAD.Geometry.PlanarEntity
        Autodesk.AutoCAD.Geometry.Sphere
        Autodesk.AutoCAD.Geometry.Torus

Public abstract Class Surface
Inherits Entity3d

public abstract class Surface : Entity3d;