84 TRACHELIPODA. 



FAMILY V, lANTHINA. 



Animal capable of raising the shell itself to the surface of the 

 water, and floating. 



Genus 54-.— lANTHINA.— Xawiarc^. 



Generic Character. — Shell ventricose;, conical,, thin, and pel- 

 lucid ; aperture triangular ; columella straight, produced beyond 

 the base of the outer lip ; the lip, or middle sinus, emarginate ; 

 aperture without an operculum. 



lanthina communis. — The Common Ianthina. Plate XII. 

 fig. 19. Extremely fragile, of a beautiful violet hue ; aperture 

 triangular, with a small notch on the margin of the outer lips. 

 One inch long. Inhabits the Atlantic and Mediterranean. 



FAMILY VI. NERITACEA. 



The shells are both marine and fresh- water ; semiglobular or 

 oval ; destitute of a columella, and the aperture edged and trans- 

 verse, and provided with an operculum. 



Genus 55.— NA TIC A.— ^cfanson. 



Generic Character. — Shell subglobose, umbilicated ; aperture 

 entire, and half rounded ; outer lip oblique, without teeth ; with 

 a callosity, which partly covers the umbilicus, and in some species 

 entirely covers it ; outer lip sharp, smooth within ; aperture 

 provided with an operculum. 



Natica canrena. — The Canrena Natica. Plate XII. fig. 

 15. Subglobular, smooth ; fawn-coloured, with bands and in- 

 terrupted rays of reddish-brown, and zigzag lines and streaks ; 

 base of body and inner lip white, deeply umbilicated ; spire a 

 little prominent. One inch and three-fourths long. Inhabits 

 the West Indian ocean. 



Genus 56 NERITA.—ZawwrcA. 



Generic Character. — Shell solid, semi-globose, flattened be- 



