406 
MOLLUSCA. 
the base of the outer lip ; the lip, or middle sinus, emarginate; 
aperture without an operculum. 
Ianthina communis. — The Common Ianthina. 
Plate LXXXV. fig. 19. 
Extremely fragile, of a beautiful violet hue; aperture trian¬ 
gular, with a small notch on the margin of the outer lips. One 
inch long. Inhabits the Atlantic and Mediterranean. 
TRIBE 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. —NATICA.— Lamarck. 
Generic Character. — Shell subglobose, umbilicated ; aperture 
entire, and half rounded; outer lip oblique, without teeth; with 
a callosity, which partly covers the umbilicus, and some species 
entirely covers it; outer lip sharp, smooth within ; aperture pro¬ 
vided with an operculum. 
Natica canrena .— The Canrena Natica. 
Plate LXXXV. fig. 15. 
Subglobular, smooth; fawn-coloured, with bands and inter¬ 
rupted rays of reddish-brown, and zigzag lines and streaks; base 
of body and inner lip white, deeply umbilicated; spire a little 
prominent. One and three-fourth inches long. Inhabits the 
West Indian Ocean. 
Genus 56. —NERITA.— Lamarck. 
Generic Character _Shell solid, semiglobose, flattened be¬ 
low, without an umbilicus ; aperture semiorbicular and entire ; 
inner lip flattened, septiform, acute, and frequently dentated or 
crenated on the inner edge of the lip; outer lip obtuse, and of¬ 
ten provided internally with teeth. 
Nerita peloronta. — The Monstrous Nerita. 
Plate LXXXV. fig. 13. 
Thick, transversely sulcated; ash-coloured, or reddish-yellow, 
with variously coloured bands ; inner lip with two crenulations. 
