This is an unusual ammonite from the ‘middle’ part of the Jurassic period, a time when many ammonites developed into different forms. In this case, the outer whorls enveloped the inner ones to create a football-like shape. The suture lines (wavy patterns) are just visible, made where the internal chamber walls met the shell.
The fossil was found in the Cordatum Zone, Jordan Hill Clay, about three metres below the Red Nodule Bed.