514 
MOLLUSCA. 
THE POLISHED NERITA. 
THE NERITID^. 
This is a small family, the typical species of which, Nerites ustulata, are called Sea-Snails : 
they have a thick and rather globose shell, and are mostly 
marine ; those of the genus JVeritina, however, inhabit fresh 
water. The Polished Nerita, JVerita polita, is distrib- 
uted through nearly all tropical seas. 
THE PALUDINID^. 
This family includes several genera, having somewhat glo- 
bular shells, with a thick olive-green epidermis. The Eiver- 
Snail, jPaludina Listeria has a turbinated shell, with round 
whorls. Found in the Caspian and Black Seas. The Ap- 
ple-Snail or Idol-Shell, Ampullaria glohosa, has a globular shell and a large ventricose body- 
whorl; found in the "West Indies, South 
America, &c. The A. duhia is found in the 
Nile. Several species of this genus, brought 
from Egypt to Paris packed in bran, were 
found living, though they had been four 
months in making the passage. 
THE NATICIDJE. 
In these the shell, which is globular, com- 
posed of five whorls, and has an entire aper- 
ture, is partially inclosed in the mantle. The 
Natica canrena, found in various seas, is 
blind ; it frequents sandy and gravelly bot- 
toms, ranging from low water to a depth 
of ninety fathoms. 
THE lANTHINIDiE. 
These are carnivorous and oceanic, and 
possess shells almost exactly resembling 
those of the land-snail; they are without 
eyes, and secrete a sort of operculum, which 
operates as a float, bearing them about upon 
the water. They occur in vast numbers in 
the Atlantic, and are sometimes driven by 
storms upon the coasts of Great Britain ; 
the same happens on our shores. In 1839, 
great numbers of them were Avashed upon 
the beaches of Nantucket. 
THE CALYPTRiEIDiE. 
These, called Bonnet Limpets, have a lim- 
pet-like shell, which is usually somewhat 
spiral at the apex ; they appear to pass a 
sedentary life, attached to stones and rocks. 
Of the widely distributed genus Calyptrxa, 
of which the Cup-and-Saucer Limpet, C. 
equestris, is the type, fifty species are known. 
THE HALIOTID^. 
In these, which are called Ear-Shells, the 
animal has a short muzzle and two branchial plumes ; the shell has a spiral conformation, and the 
perforations for the anal siphon are arranged in a row along the back of the shell. The Tuber- 
THB AMPULLAEIA DDBIA. 
THE EAR-SHELL. 
