This speciment was HUGE at 11.5cm but if it was entire, maybe add another 1-2cm. The image from Mr Lutaenko's work is included to show a C.labiata that is 12.45cm despite wiki and other places saying they grow to 10cm.
Since it is brown inside, has thick teeth and I can't see the shelf (or ledge or "Myophoric flange") I went with C.labiata. But really none of my fragments correspond exactly to the photos or descriptions I have seen from other countries.