68 TABLE OF GENERA. 



*** Shell smooth, half-ovate ; mouth half circular ; inner lip 



transverse, acute. 

 1. NERITINA. 



c. Shell moderately thick ; edge of lips more or less thickened 

 and reflexed. 



* Mouth transverse. 



1 0. HELIX. Shell suborbicular or conical ; mouth lunate, or ovate 

 or circular. 



* * Mouth oblong, longitudinal. 



13. BULIMUS. Shell oblong, striated ; mouth toothless. 

 14*. ZUA. Shell oblong, polished; mouth margined, tooth 



less. 

 15. AZECA. Shell oblong, polished ; mouth margined, toothed. 



21. CARYCHIUM. Shell oblong, smooth, white ; mantle oblong, 

 margined, sinuous. 



23. CONOVULUS. Shell oblong, smooth; mantle narrow; pil- 

 lar obliquely plaited. 



17. PUPA. Shell subcylindrical, striated, blunt ; mouth margined, 



mostly toothed. 



18. VERTIGO. Shell subcylindrical, striated, blunt ; mouth 



dextral or sinistral, margined, mostly toothed. 



19. BALEA. Shell turreted, striated; apex acute ; mouth sinistral, 



not plaited. 



20. CLAUSILIA. Shell fusiform, striated; apex acute; mouth 



sinistral, plaited. 



E. Shell discoidal ; whorles revolving nearly on the same line. 

 * Mouth lunate, sinistral, edge not continued. 



30. PLANORBIS. Cavity simple. 



31. SEGMENTINA. Cavity crossed with transverse ridges. 



* * Mouth circular, dextral, edge continued. 



% 

 5. VALVATA. 



