This is a close up scan of the cracked ear variety.
To me, it appears as a thin-edged circle with a solid blob in the top half and just a partial outline of the bottom arc of the circle.

This is a second stamp with what appears to be a complete thin-edged circle without the solid blob in the top half and a more complete bottom arc.

Both marks are in the same area of the ear and both have a single dot in the centre of the circle.
Is it possible that mine is a variation of the true variety?
Any comments would be appreciated.