1849.] 



SHARPE ON THE GENUS NERIN^A. 



103 



only, as the perforation of the columella is not accompanied by any 

 other constant character, and the umbilicated and non-umbilicated 

 species can hardly be distinguished ; moreover N. Voltzii of Des- 

 longchamps has the columella solid when young and perforated in 

 its older stages. More than half the known species of Nerincea fall 

 into this division. 



Fig. 1 is the section of a portion of i\^. Archimedis, D'Orb., from 

 near Cintra, which illustrates the internal characters of this sub- 

 genus. 



Fig. 2. 



Fig. 1. 



Subgenus 2. Nerinella. 



Columella solid, either simple or furnished with one fold; the 

 outer lip with one internal fold ; folds simple ; the mouth usually 

 much longer than wide ; the shell nearly cylindrical or very taper. 



The species of this section are not numerous ; they have not the 

 characters laid down by the founders of the genus, but are obviously 

 closely related to it : they are usually small and very elongated. 



Fig. 2 represents a section of part of iV^. Dupiniana, D'Orb., copied 

 from the * Paleontologie Fran9aise ' to illustrate this subgenus. 



Subgenus 3. Trochalia*. 



Columella umbilicated, with one fold ; mouth rhomboidal ; the 

 outer lip either simple, or thickened internally, or furnished with 

 one internal fold ; folds simple ; the shell usually short and co- 

 nical. 



These species differ widely from the original type of the genus, 

 and approach the Trochi ; they are usually of large size, without any 



* Named fi'om its resemblance to Trochus. 



TpoxaXia, a water-wheel. 

 I 2 



