HELIX. 
103 
also to show the natural groups into which the 
numerous exotic species naturally fall. 
The size of the land Mollusca and their shells are 
very subject to variation, according to the quantity 
of food they can procure and the temperature of the 
district they inhabit. Those inhabiting the warmer 
countries are generally larger than those which in- 
habit a colder climate, produced either by geographic 
position or a more elevated situation in a southern 
latitude. The small size in the latter instance is 
probably caused by the animal being for a longer 
portion of the year in a torpid or hibernating condi- 
tion. 
a. Shell suhglohose banded ; peristome rather thickened ^ 
rejiexed^ with an internal rib ; axis perforated^ 
perforation covered in the adult specimens; epi- 
phragm membranaceous. Jaws strong^ toothed. 
(Acavus Montf. Tachea Leach.^ 
34. 1. Helix aspersa. Common Snail. — Shell 
somewhat globular, with the surface wrinkled, 
yellowish-brown or olive, with four brown 
bands ; whorls four ; mouth roundish lunate ; 
the peristome white and reflected, (t. 4. f. 35.) 
Helix aspersa. Muller^ Verm, ii. 59.; Montagu^ p. 407.; Drop, 
p. 89. tab. 5. f. 23.; Brard,^ p. 7. tab. 1. f. 1. ; Turton^ Mann. 
52. f. 35. ; Leach., Syn. Moll. 60. t. 2. f. 1, 2. ; Jeffreys., Linn, 
Trans, xvi. 328.; Forbes and Hanley., B. M, iv. 44. t. 116. 
f. 1. — Helix hortensis. Penn. Zool. iv. 136. t. 84. f. 129.; 
Donovan, Turt. Diet. p. 60. — Helix grisea. Linn., 
S. N. 1247.; Dillwyn, p. 943. — Helix lucorum. Pulteney. 
Cat. Dors. 943. — Cochlea vulgaris. Da Costa, p. 72. t. 4. 
f. 1. — Helix variegata. Gmelin, S. N. 3650. — Coenatoria 
H 4 
