1.   Only the distal edge of the radial shields are visible.

2.   The radial shields are also covered with rugose granules but it is possible to distinguish their position on the disk.

3.   The radial shields are not visible, probably absent.

4.   The radial shields are oval, usually naked in all but the largest specimens.

5.   The radial shields are short and bar-like and carry a single row or well developed spinelets along their length.

6.   The radial shields are triangular to tear-drop shaped, just over a quarter the disk radius in length.

7.   The radial shields are usually covered although in some specimens it is possible to see the outline of distal end.