PLATE XXV. 



Zone of Arietites JBucMandi, superior. 



Fig. 1. Aegoceras planicosta, Sowerby. Natural size. This specimen represents a 



large Am. Dudressieri, cV Orbigny, which 

 is in reality the adult form of Aegoceras 

 planicosta, Sow. This magnificent speci- 

 men belongs to the Royal School of Mines, 

 and was collected at Lyme Regis. 



2. — — — A portion of the outer lamina of the shell, 



showing lines and perforations highly 

 magnified. 



3. — Showing parallel lines formed by a fine 



punctated surface. 





