GENERA OF SHELLS. 79 



P. bulimoides, rubens, variegata, elegans, Peruviana, ne- 

 bulosa, sulcata, Mauritiana, angulifera. 



TuRRiTELLA. Shell lurreted, not pearly ; 

 aperture rounded, entire ; lips disunited above, 

 the right having a sinus. Operculum horny. 



Distinguished from turbo by the general form of the 

 shell and by the sinus on the right lip, a constant 

 character. Most of the species are transversely carin- 

 ated or striated, but none of them have vertical ribs, 

 varices or tubercles. 



T. duplicata, terebra, imbricata, replicata, fuscata, cornea, 

 brevialis, bicingulata, trisulcata, exoleta, carinifera, australis, 

 Virginiana, — concava, sequalis, alternata, reticulata, im- 

 pressa, bisuturalis. 



Sect. IL— TRACHELIPODA ZOOPHAGA. 



Shell spirivalve, ensheathing : aperture either canaliculate^ 

 notched or inclined at the base. 



CANALIFERA. 



Shell with a caned more or less long at the base of the 

 aperture, the right lip of which does not change its 

 form hy age. 



DiV. I. No CONSTANT VARIX ON THE OUTER LIP. 



Cerithtum. Shell turreted ; aperture ob- 

 long, oblique, terminated at its base by a short 

 canal, truncated or recurved, never emarginate. 

 A slight channel at the upper extremity of the 

 lip. Operculum, small, orbicular, horny. 



The spire of the shell constitutes at least two thirds 



