346 
MOLLUSCS. 
further forward. In the present genus there is no internal shield-like shell, as 
in Limax, but this is represented by a few unequal calcareous particles beneath 
the mantle. Nine species of this genus are said to occur in Britain, and of these 
the large A. empiricorum is the commonest and best known. It is sometimes 
intensely black, but it may be brown, red, yellow, greenish, or even white. This 
great variation in colour is unaccountable, for black and red specimens occur in 
the same districts where the natural surroundings are practically the same. The 
edge of the foot, when crawling, displays a yellowish or orange border crossed by 
closely-set black lines. This species usually feed on vegetable substances, but it has 
occasionally been known to devour earthworms. It ranges over a considerable 
part of Europe, and has been recorded from Siberia, Corsica, and as far as Madeira. 
The genus Helix includes the true snails of the type represented by the 
garden-snail ( H '. aspersa ), and the edible or vine-snail ( H. pomatia), as it has been 
variously named. The animal is completely retractile within its shell, and the 
body distinct from the foot, and well protected by the spiral shell. The breathing- 
orifice is on the right side beneath the margin of the aperture of the shell. The 
genus Helix, as understood at the present time, is much more limited than it was 
some years ago, and the tendency of conchologists is to propose still further 
limitations. The necessity of dividing an enormous genus like Helix containing 
thousands of species, is universally recognised, but the danger arises of carrying 
this sectionising too far. Many of the divisions are partly founded upon 
geographical considerations. The form of the shell in Helix is extremely variable, 
as a glance at any collection will show. Some are sharply conical, others globular, 
or flat and acutely keeled at the circumference; and the variety of colour is 
endless, and changeable in specimens of the same species. The British H. nemoralis 
and H. hortensis are striking examples; and II. picta , a beautiful Cuban shell, is 
another remarkable instance. Not only does the ground-colour offer many 
variations, but the colour and disposition of the spiral lines or bands which adorn 
the surface are equally variable. The twenty-five species of Helix which occur 
in Britain are insignificant in comparison with their exotic relatives, although 
large enough to do a considerable amount of damage in the garden. The finest is 
the H. pomatia, popularly known as the apple-snail, but this name, as pointed 
out by various writers, although appropriate as regards its shape, was not derived 
from the Latin pomum, an apple, but from the Greek poma, signifying a lid or 
operculum. When winter is approaching, the animal secretes a diaphragm or 
covering to the aperture of the shell, a false operculum, to keep out the cold and 
wet when hibernating under ground. It is composed of slime and calcareous 
matter, but is not pierced with a minute breathing-hole, as is the case in some 
other species, although probably sufficiently porous to permit of whatever change 
of air may be necessary during the winter sleep. The eggs of H. pomatia are 
deposited in June in holes in the ground, formed by the snail itself. They are 
about the size of a small pea, and much resemble in colour and consistency the 
berries of the mistletoe. Only a day or two is occupied in the production of sixty 
to eighty eggs, and these are then covered up with earth and the ground so 
levelled that the place, or egg-nest, is difficult to discover. The length of time 
before hatching varies according to locality and the state of the temperature. It 
