This .NET enum wraps the AcDb::SubentType ObjectARX enum. 

An entity can be composed of many graphic subentities, such as arcs, lines, text, vertices, edges, faces, etc. This class creates subentity IDs using one of these subentities and an index. The index is the graphics system marker for the subentity.

Public Enum SubentityType
  Null
  Face
  Edge
  Vertex
  MlineCache
  Class
End Enum

public enum SubentityType {
  Null,
  Face,
  Edge,
  Vertex,
  MlineCache,
  Class
}