38 



in fact, the edible snail seen in the markets of Italy and the 

 South of France, it is found on tlie chalk, soil about Dork- 

 ing, and Leatherhead, but I do not know that it is to be 

 met with in this part of the country. The smallest British 

 species is the helix pygma, not larger than a grain of 

 mustard seed. Another minute species is the Helix Pispida, 

 a hairy snail, is to be met with about the Shakespear 

 Cliff. The Helix Pomatia is far exceeded in magnitude by 

 the snails of the tropics, though none of them are of large 

 size, but two other genera of this family, the Bulimus and 

 Achatina, become large shells, especially some African 

 species of Achatina. Here is one from Zanzibar, which 

 from its size and solidity would not readily be taken for a 

 snail, but such it is and there are larger specimens in the 

 British Museum. The snails have no Operculum, but they 

 make a temporary enclosure for themselves during the 

 winter, when they are torpid. The common brown snail 

 fills the aperture of its shell with a glutinous substance. 

 The Helix Pomatia forms a calcareous plate. Another 

 family of land shells, the Cyclostomidse, are operculated. 

 There is one species of Cyclostoma the typical genus of this 

 family in Great Britain, it inhabits chalky soils, and I 

 mention it here because it is to be found on the East Cliff. 

 I am afraid T have already broken bounds beyond the time 

 usually allotted to these little discourses, and must say but 

 very few words about the Conchifera. The shell of the 

 Conchifera is formed in the same manner as that of the 

 Gasteropoda, that is to say by secretion from the mantle of 

 the animal, but the action is more simple, be- 

 ing in a direction forward from the original 

 Bhell of the infant mollusc, which finally becomes the 

 apex of the adult shell, and called the Umbo, nevertheless, 

 as in the Gasteropoda, the action of the mantle is more en- 

 ergetic in one part than in another ; hence, as a general 

 rule, the Umbo, is not in the middle of the shell of which 

 a greater part is behind the Umbo, than in front of it, as 

 may be conspicuously seen in the Tapes. Moreover, 



