MOLLUSCA OR UNIVALVES. 257 



of them have a small tooth at the lower part 

 of the right lip. When the animal is alive, 

 the shell is covered so much by the foot 

 that only the middle of the back can be 

 seen. The Ancillaria cinnamonea is exceedingly 

 scarce. 



124. Oliva. — Shell oblong, smooth, and 

 convolute; spire short; sutures channelled or 



grooved ; mouth narrow and long ; right lip 

 rather sharp ; left lip thickened at the top, and 

 striated ; operculum horny and small in some 

 species, in others not existing.* Animal, head 

 small, terminated by a proboscis ; two tentacula 

 enlarged at the base, and having the eyes si- 



* Gray. 



S 



