UNIVALVES NERITA. 173 



NERITA Nerite or Hoof-Shell. 



DESCRIPTION OF PLATE XXX. 



DiT. I. —Fam. 1. Fig. 5. N. vitellus. 



Fam. 2. Fig. 6. N. canrena. 



Fam. 3. Fig. 4. N. albumen. 

 DiT. II.^Fam. 1. Fig. 2. N. corona. 



Fam. 2. Fig. 3. N. fluviatilis. 

 Dnr.III — Fam. 2. Fig. 1. N. polita. 



Fam. 2. Fig. 7. N. peloronta. 



Shell univalve, spiral, gibbons; aperture semiorbicnlar or semi- 

 lunar; pillar-lip transversely truncate, flattish. 



THERE is considerable variation in the form and 

 markings of the Neritae: some are spiral, with promi- 

 nent Avhorls ; others have their whorls partly or wholly 

 concealed: some again are umbilicated, while others 

 are perfectly entire and solid ; and many have the um- 

 bilicus partially covered by a repand lip, or fissurated 

 nodule. 



The back of the shell is sometimes covered with 

 strong, elevated ribs; and in a few species with 

 spines; it is often only minutely striated, and has 

 frequently a perfectly smooth surface, and a brilliant 

 polish. 



Among those species which are umbilicated, and form 

 the first division, may be mentioned the N. vitellus, N. 

 canrena, (of which there are many beautifnl varie- 

 ties), N. cancellala, N. glaucina, and N. mammilla: 



