Alternatively... in the Insert tab, choose Shapes, and click on the
semi-circle in the 2nd row of Basic Shapes, 4 from the left.
If you want it to be a line semicircle instead of multidimensional, drag the
yellow handle to the left so that the inner and outer walls become a line.
If you want more or less of the circle arc, drag the yellow handle in an arc
to increase or decrease the arc. Use the green handle to rotate the arc, and
the other handles to expand and/or stretch/distort the arc.
And remember, no more than two of each kind of animal are allowed on the
arc. No, wait... that's ark. ;-)