From the Jurassic, Lower Sinemurian, Obtusum Zone SI1B.
Collected from Lyme regis,Dorset,England.
Superb 3d specimen from this classic location ,with some nice negatives on the front and a smooth shelled microconch of another Arnioceras.
The Ammonites measure 35mm and 15mm respectively.
And with the base cut matrix is 112mm x 73mm.