102 PALEONTOLOGY 



27 to the axis of the spire ; the anterior canal is nearly 

 straight, but with a slight twist which tends to bring it 

 more in line with the spire-axis, about two-thirds the 

 length of the aperture proper, and nearly half its width. 

 The shell is imperforate. Having an anterior canal it is 

 siphonostome, Natica and Tiirritella being holostome. 



Many species differing in details of ornament from 

 C. senattim will equally well illustrate the genus in the 



AC 

 FIG. 29. CERITHIUM SERRATUM, LAMARCK, EOCENE, (x^.) 



A.C., Anterior canal ; I.L., inner lip ; O.L., outer lip ; S, suture. 

 Details omitted near apex. (After Deshayes.) 



broad sense. The original genus Cerithium has now been 

 split up into numerous smaller genera. Recent species 

 are all marine, and though the group is world-wide, the 

 most typical species are tropical. The genus is known 

 fossil from the Jurassic upwards, and had a wide geo- 

 graphical distribution until at least the Miocene period. 



