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 subglobose banded ; peristome rather thickened, 

 reflexed) 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, t.,131. ; 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. Ccenatoria 

 H 4 



