GASTEROPODA. 



75 



The northern seas must ever have been inclement, and the 

 tropical seas always tropical ; but the latitude of England 

 being most liable to vicissitudes of climate, might be expected 

 to show the greatest variety, and the most complete and rapid 

 alterations of organic life. In the London clay are found many 



Fig. 19. 



Tertiary Univalves. 



Nautilus (Aturia) zic-zac, Sby. ; Eocene, Britain. 



Nautilus zic-zac, front view of a septum. 



Conorbis dormitor, Sol. ; Eocene, Britain. 



Borsonia lineata, T. Edw. ; M. Eocene, Hants. 



Volutilitlies luctator, Sol. ; Eocene, Britain. 



Natica (Desbayesia) cochlearia, Brongn. ; Eocene, N. Italy. 



Turritella (Proto) cathedralis, Brongn.; Miocene, Bordeaux. 



8. Nerita (Velates) perversa, Gm. ; Eocene, France. 



9. Helix (Lychnus) Matheroni, Beq. ; Eocene, S. France. 



10. Ferussina tricarinata, M. Br. ; Miocene, Hockheiin. 



11. Volvaria bulloides, Lam. ; Eocene, Grignon. 



12. Vaginella depressa, Bast.; Miocene, Bordeaux. 



species of Clavella, Typhis, Mitra, Pseudoliva, Oliva, and Ancil- 

 laria ; and some extinct forms (Lciostoma and Strcpsidura) 

 related to Fusus. The middle tertiary, wanting in England, 

 but largely developed in Central and Southern Europe, also 

 contains many genera belonging now to warmer latitudes, and 

 many species still living in the south. In the newer tertiaries 

 of Europe these southern forms disappear, and are gradually 



