This .NET class wraps the AcDbDgnUnderlayItem ObjectARX class. It represents underlay items.

Autodesk.AutoCAD.DatabaseServices.UnderlayItem
    Autodesk.AutoCAD.DatabaseServices.DgnUnderlayItem

Public Class DgnUnderlayItem
Inherits UnderlayItem

public class DgnUnderlayItem : UnderlayItem;