Adding a MetaClass to a Metamodel Diagram
To add an existing MetaClass to a metamodel diagram:
1. In the metamodel diagram insert toolbar, click MetaClass 
then click in the diagram.
then click in the diagram.The Add Concrete MetaClass dialog box appears.
2. In the Name field, click the arrow and select List.
3. In the list, select the required MetaClass.
4. Click OK.
The MetaClass name is displayed in the Add Concrete MetaClass dialog box.
5. Click Connect.
The MetaClass is added to the metamodel diagram.
You can access the attributes of the MetaClass by opening its Properties window.
In the same way you can place several MetaClasses in the metamodel diagram.