CERITHIUM. 



4. Having a very short canal and a prominent callo- 

 sity at the posterior part of the inner lip. Fig. 4. 



5. With a thickened but not reflected outer lip, 

 scarcely any canal, and forming frequent varices. Fig. 5. 



6. With a rugose exterior, a distinct callosity at the 

 posterior part of the inner lip and a rather lengthened, 

 nearly straight canal ; one varix opposite to the aperture. 

 Fig. 6. 



7. With the outer lip scarcely thickened, while the 

 inner lip is somewhat extended and thickened; a rather 

 lengthened canal distinctly reflected; and frequently a 

 fold at the centre of the columella. Fig. 7, 8. 



8. With a short and very wide canal, equal in length 

 on both sides, the outer lip somewhat dilated towards the 

 anterior part, and a single row of tubercles externally. 

 Fig. 9. 



9. Potamis. Fig. 10. 



Of each of the above peculiar forms we have repre- 

 sented a species. 



Fig. 1. is Cerithium breviculum, nobis. 



2. decollatum 



3. sulcatum. 



4. = tuberculatum ? 



5. ■' varicosum, nobis. 



6. ~ mutatum. 



7. ... Columna, nobis. 



8. Clava, Gray. 



9. pacificum, nobis. 



10. ' muricatum. 



