GroupType

public void GetInfo_GroupType(GroupType groupType)
{
    string message = "GroupType";
    //Retrieve a set of all the groups that have this type.
    foreach (Group group in groupType.Groups)
    {
        // Get GroupType group name
        message = "\nThe group type name is : " + groupType.Name;
        //Returns all the members of the group.
        message += "\nThe types and ids of the group members are : ";
        IList<ElementId> groupMembers = group.GetMemberIds();
        foreach (ElementId memberId in groupMembers)
        {
            Element element = group.Document.GetElement(memberId);
            // Get GroupType group element id
            message += "\n\t" + element.GetType().Name + " : " + memberId.ToString();
        }
    }
    TaskDialog.Show("Revit",message);
}