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. empiricorwm 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. pomaiia), 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 H 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 



