PLATE XXIII. 



Zone of the Arielites Bucklandi, superior. 



Fig. 1. Aegoceras Birchii, Soiverby. Side view, natural size. 



2. — — — Siphonal area, showing the fine polytome ribs 



crossing this area. 



In this magnificent specimen in my collection the shell is well preserved throughout, 

 so that the sharpness of the tubercles and the delicacy of the sculpture on the ventral 

 area are well displayed. 



