134 On the Inferior Oolite and Lias of Northamptonshire 3 



Rostellaria (abundant), Cidaris*, Nucula, Avicula, and 

 Aptychus. These are succeeded by two or tbree blue marly 

 bands divided by shale, which contain a univalve like a Ceri- 

 thium, Avicula, Nucula, Pholadomya, Pecten, Astarte, and Am- 

 monites. A light blue, slightly indurated marl reposes imme- 

 diately upon the Marlstone. The total thickness of these clays 

 and marls forming the base of the Upper Lias is about 30 feet. 



* A similar small species of Cidaris ( C. minuta) occurs abundantly with 

 spines attached in the Upper Lias shale at Gretton near Winchcomb, where 

 a fine specimen of a Lepidotus was lately discovered in the * fish bed,' and 

 is now in the collection of my friend Dr. Wright. 



