162 UNIVALVES —_ HELIX. 
woods of Europe, and was first introduced into this 
country by Sir Kenelm Digby, for medical purposes. 
The animal (which was considered a luxury by the 
Romans) is oviparous, and very tenacious of life; to= 
wards winter it covers its aperture with a calcareous 
lid, resembling an operculum, and remains in a torpid 
state until the spring. 
The shells of the fourth division have a ventricose 
form, and resemble those of the sixth division of the 
genus Bulla, as is there observed. The H. ovalis 
and H. oblonga arethe most characteristic; the eggs 
of the animal are perfectly elliptical, and are nearly 
the size of those of the common sparrow. 
The H. amarula of the fifth division is the only co- 
ronated species of the genus. 
The shells of the sixth division are very globose, and 
have their whorls much produced: the H. ampullacea 
may be referred to as an example. 
The animal of the H. ianthina, of the eighth divi- 
sion, has the property of emitting a phosphorescent 
light, and_ stains the hand of a purple color, not easily 
removed: they are found in great numbers, floating on 
marine substances. 
The eleventh division contains those species which 
are usually found in stagnant waters; they have a ven- 
tricose form, and are remarkably fragile and pellucid. 
This genus has also its turreted class, forming the 
twelfth division. The H. decollata and H. columna are 
illustrative of the two families. 
The most rare and beautiful species are the H.ringens, 
H. tricarinata, H. otis, H. heemastoma, and H. columna. 
There are many species of this genus which inhabit 
