250 



HUGH WATSON. 



ganglia, is probably one of the most recently evolved genera 

 of the Oleacinidas. Indeed, its distribution suggests that it 

 may not have arisen until after the final separation of the 

 West Indian Islands from the mainland. I think that most 

 zoologists who have studied the Oleacinidge will agree that 

 the most primitive genera in the family are those with long 

 spires, namely Spiraxis, Pseudosubulina, and Vari- 

 cella. These genera are very unlike Achat in a, but they 



Text-fig. 7. 



2b 



J4. 



A. Curvella caloraplie Presiow, Brit. E. Africa. 

 B. "Varicella nemorensis ^cZs., Jamaica. 



Representative teeth from the radula. x 400. 



are exceedingly similar to the more primitive members of 

 the A cliatinidai, if we include the Stenogyrinas and 

 Coeliaxin^e in that family. It is, in fact, almost impossible 

 to say whether some groups of species should be placed in 

 the Stenogyrinae or Oleacinid^e until their radula has 

 been examined. I believe, therefore, that the Oleacinid^e 

 have been derived from gnathophorous snails closely allied 

 to the Stenogyrinai or even belonging to that subfamily. 



The chief differences between the internal au atomy of the 

 Stenogyrinae and that of the OleacinidaD are to be found 

 in the radula. We know, however, that the Stenogyrinas 



