UNIVALVES — NERITA 99 



In most species the back of the sliell is covered witli 

 strong, elevated ribs, sometimes nodulous and imbricate ; 

 in others the shell is only minutely striate; and in many 

 the surface is so perfectly smooth as to afford a brilliant 

 polish. 



Among those species vrhich are umbilicate the follow- 

 ing may be quoted : viz. Nerita Canrena or Tabby-cat 

 Nerite, (of v«rhich there are many beautiful varieties), Ne- 

 rita Cancellata, Nerita Glaucina, Nerita Vitellus, and 

 Nerita Mammilla, commonly known by the name of the 

 Breast Snail. The most usual variety of this shell is that 

 which is entirely white, having a china-ware-like appear- 

 ance ; but the rarer sorts are those which incline to a 

 brownish orange, having their lips surmounted with a 

 black margin or border. 



The Nerita Stercus-muscarum, or Fly-spot Nerite, is 

 beautifully dotted with brown, or rufous, on a clear white 

 ground. The Nerita Fulminea, instead of being dotted, 

 is striped angularly, something in resemblance of forked 

 lightning. The Nerita Rugosa is rough or wrinkled, and 

 the Nerita Sulcata has its whorls obliquely plaited. 



The next species of Nerites are those which are imper- 

 forate, being at the same time toothless; among them 

 may be ranked the Nerita Corona, or Crowned Nerite : 

 this shell is often of a blackish color, and has its whorls 

 crowned with shorter or longer spines. The Nerita Flu- 

 viatilis also belongs to this division; it is an inhabitant of 

 the rivers of Europe and Barbary, and is usually mark- 

 ed with scaly spots, sometimes rugged, streaked, or reti- 

 culate. The Nerita Littoralis is found on the rocks of 

 most European shores; and the Nerita Lacustris delights 

 in the still waters and warm springs of Europe. 



Those Nerites which come next in succession, are sucii 



