public EllipticArcBuilderEx( 
   MapPoint startPt,
   MapPoint endPt,
   Coordinate2D centerPt,
   ArcOrientation orientation,
   SpatialReference spatialReference
)

// Construct a circular arc from (2, 1) to (1, 2) 
// with center point at (1, 1) and orientation counterclockwise.
// Use a builderEx convenience method or use a builderEx constructor.

MapPoint toPt = MapPointBuilderEx.CreateMapPoint(1, 2);
MapPoint fromPt = MapPointBuilderEx.CreateMapPoint(2, 1);
Coordinate2D centerPtCoord = new Coordinate2D(1, 1);

// BuilderEx convenience methods don't need to run on the MCT.
EllipticArcSegment circularArc = EllipticArcBuilderEx.CreateCircularArc(fromPt, toPt, centerPtCoord, ArcOrientation.ArcCounterClockwise);

// BuilderEx constructors need to run on the MCT.
EllipticArcBuilderEx cab = new EllipticArcBuilderEx(fromPt, toPt, centerPtCoord, ArcOrientation.ArcCounterClockwise);
EllipticArcSegment otherCircularArc = cab.ToSegment();

//Must be on QueuedTask.Run(() => { ...

//Build geometry
Coordinate2D center = new Coordinate2D(4.5, 4);
var eabCir = new EllipticArcBuilderEx(center, 0.5, ArcOrientation.ArcClockwise);
var cir = eabCir.ToSegment();

var poly = PolygonBuilderEx.CreatePolygon(
  PolylineBuilderEx.CreatePolyline(cir, AttributeFlags.AllAttributes));

//Set symbolology, create and add element to layout
CIMTextSymbol sym = SymbolFactory.Instance.ConstructTextSymbol(
                ColorFactory.Instance.GreenRGB, 10, "Arial", "Regular");
string text = "Circle, circle, circle";

GraphicElement cirTxtElm = ElementFactory.Instance.CreateTextGraphicElement(
  container, TextType.CircleParagraph, poly, sym, text, "New Circle Text", false);