NATICKS. 187 
the most part they are marine, but some inhabit 
rivers and lakes of fresh water; and M. Lesson 
affirms of one species which is found in Australia, 
that it lives abundantly on trees. Some of the 
Neritine are ascertained, on indubitable authority, 
to live indifferently in the sea and in fresh-water. 
GENUS NATICA. 
Handsome globose shells, with a smooth surface 
as if varnished, and with a very wide aperture, 
compose this genus, which is technically distin- 
guished by having the inner lip smooth, not 
depressed; the umbilicus open, with a central 
gibbous ridge or prominence, and the operculum 
formed of shelly substance. 
The animal is large, slimy, and slug-like, with 
the foot so enormously developed as to communicate 
to the creature a most remarkable aspect when 
seen crawling. It is a long oval plate of soft flesh, 
commonly squared in front, and rounded or notched 
behind. ‘The forepart, where it is widest, forms a 
thick sort of shield, somewhat eared, which is 
turned up on the front of the shell, partially 
covering it, and hiding the whole head of the 
animal, except the tentacles, which project from 
behind it. The hind part of the foot, and the 
sides also, partially envelope the shell, of which 
only the summit is seen, apparently embedded in 
an immense mass of white flesh. The operculum, 
notwithstanding its large size, is not visible when 
the animal is in motion, beimmg hidden by the 
extremity of the shell. 
When one beholds the great volume of fleshy 
substance which the animal displays when crawling, 
