From the center draw two lines (E) at an angle and one line (F) vertically.
If the cone is cut off vertically on the dotted line, A, the curve is a hyperbola.
Then he enlarged the hole and slightly deepened it vertically.
Basal ring violin-shaped, with ten to twelve flat lamellar, vertically descending feet, about as long as the ovate sagittal ring.
This point is marked by ...