GASTEROPODA. 



"which the shell of the adult has its outer lip furnished with 

 long claws, one of which forms a posterior canal close to the 



Fig. 386. — Pteroceras oceani. Neocomian. 



spire. INIany fossil species are known, commencing in the 

 Lias. 



In the genus Rostellaria (fig. 387), 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 B. ampla (fig. 

 387) of the London Clay (Eocene). Lastly, the genus Sera/phs 

 comprises smooth shells, with a short or obsolete spire, a thin 

 outer lip, and a long narrow mouth. The fossil species date 

 from the Eocene Tertiary. 



Fam. 2. MuRiciDiE. — Shell with a straight anterior canal, 

 the aperture entire posteriorly. Eoot broad. The Muricidce 

 are essentially characteristic of the Tertiary and Eecent 

 periods. They commence, however, in the Jurassic rocks, 

 in some doubtful examples, and they are certainly repre- 

 sented in the Cretaceous rocks by not a few forms. 



In the genus Murex the canal is often very long, and 

 may be partially closed ; the shell is ornamented with Ion- 



