790 DIVISIONS OF THE GASTROPODA. 



canal close to the spire. Many fossil species are known, commenc- 

 ing in the Lias. 



In the genus Rostellaria (fig. 696), the spire is long, and has the 

 posterior canal running up it. Many fossil species are known, 

 commencing in the Cretaceous rocks. The outer lip is always 

 expanded, and in some forms is enormously so. One of the most 

 familiar species is the great R. a??ipla (fig. 696) of the London 

 Clay (Eocene). 



Lastly, in the genus Terebellum ( = Seraphs) the shell is elongated 

 and subcylindrical, with a short or obsolete spire. The aperture is 

 long and narrow, with a thin outer lip and a short canal. There is 



Fig. 6g$.—Pteroceras oceani. Neocomian. 



an emargination of the outer lip in front. The genus is Tertiary 

 and Recent, most of the fossil forms being found in the Eocene 

 rocks. 



Family 36. Cypr^eid^:. — In this family the shell is spirally 

 rolled up, but the spire is more or less completely concealed, owing 

 to the fact that the shell becomes overlaid by a coating of enamel. 

 The aperture is long and narrow (fig. 697), and is channelled at both 

 ends. The outer lip is thin in the young shell, but is thickened 

 and strongly inflected in the adult. The foot is broad, and the 

 mantle forms lobes which meet over the back of the shell. 



The principal genus in this family is Cyprcea itself, comprising 

 the numerous and well-known living shells commonly spoken of as 

 Cowries. The Cyprcece are mainly, but not exclusively, inhabi- 

 tants of warm seas, and they attain their highest development 



